cornparative- study of the rntraperitoneal Alirnentary Tractof Parasitic and Nonparasitic Larnpreys

frorn the Great Lahes Regionl2

Bv HBT,BN I. Barrr,B

Department of Zool,ogyUnhtersity of Western Ontar'io, London, Ont.

AND

KevB HeyesHrDA

Department of BiologyLakehead College of Arts, Science and, Technology

Port Arthur, Ont-

ABSTRACTThe macroscopic and microscopic anatomy of the intraperitoneal alimentary tract of two

parasitic species of lamprey, Petromyzon marinus and Ichthyomyzon unicusp,is, and two non-parasitic species, Entosphenus lamottenii and Ichthyomyzon Jossor, are described and compared.In adults of both parasitic species a diverticulum of the anterior mid-gut occurs at the level ofthe posterior oesophagus; and longitudinal mucosal folds or rugae greatly increase the internalsurface of the mid-gut. The course of the mid-gut spiral valve shows species variation, and ismore complex in parasitic than nonparasitic adults. Throughout most of the tract tall cilia occuron epithelia over the tips of folds, whereas short cilia form tracts in the fornices. Extra-epithelialtunics are composed of fibro-elastic connective tissue, circular smooth muscle, and a serosa. Thefour species can be distinguished on the bases of the mucosal folds, spiral valve, and the liningepithelium of the oesophagus.

Atrophy of the tract of both parasitic species commences with the spawning migration,when the epithelium exhibits a characteristic cytolysis with vacuolation of the cytoplasm andperipheral migration of the nuclei. ln Entosphenus lamottenii atrophy involves initial necrosisof the epithelium and subsequently of the extra-epithelial tunics, both accompanied by massiveinfiltration of lymphocytes, whereas in lchthyomyzon fossor it is resultant upon autolysis of someof the epithelial cells with progressive reduction in the diameter of the tract without interruptionof the lining layer,

INTRODUCl ' ION

SBvnner, INvEsrrcArons including Surface (1899), Gage (192$, Applegate(1950), Lanzing (1959), Vladykov and Mukerji (1961), and Sterba (t962)have noted that after the feeding period the alimentary tract of lampreysceases to function and atrophies. In some nonparasitic European species de-generative processes are initiated even during metamorphosis (Sterba, !962),and in parasitic species after cessation of feeding and coincident with the hy-pertrophy of the gonads prior to spawning (Lanzing, 1959). Most studies with

lReceived for publication September 14.1964.- zThese data in-clude a portion of a thesis presented bythe second authorin partial fulfilment

of the requirements for the Master of Science degree at the University of Westein Ontario.

J. -Frsn. RBs. Bo. ClNeoA, 2Z(2), tg6l. 289

Printed in Canada.

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290 JoURNAL ITISHERIES RESEARcH BoARD oF cANAD:\, vor'. 22, No' 2' 196s

the exception of those of Oppel (1896, 1897) and Krause (1923) have been

concerned with gross rather than histological structure and changes in the

tract. The present investigation was undertaken to compare the intraperito-

neal alimentary tracts of the ammocoetes and adults of the two contrasting

biotypes of lampreys, from both the gross and microscopical standpoints.

Two nonparasitic species, namely the Michigan brook lamprey, Ichthyornyzon

fossor Reighard and Cummins, and the American brook lamprey, Entosphenus

I,amottenii (LeSueur) were selected for comparison with two parasitic species'

the sea lamprey, Petromyzon rnarinus Linnaeus, and the silver lamprey, Ich-

thyomyzon unicuspis Hubbs and Trautman'

METHODS AND IVIATERIALS

Ammocoetes and adults of -E. lamottenii, f. fossor, and P. tnaTinus were

collected from 1956 to 1963 from Big Creek, Norfolk County, and the Saugeen

River, Southampton, Ontario. Vladykov's (1950, 1960) descriptions of larvae

were followed for identification of species. Adult I. unicuspis were taken near

Port Burwell and from the north shore of Lake Superior in 1957 and 1963.

Lampreys not fixed in the field were maintained in the laboratory in

45-gal well-aerated aquaria containing about 3 inches of river mud covered

by coarse sand, gravel, and approximately 6 inches of water. The aquaria

were given maximum exposure to sunlight to induce algal growth to provide

food for the ammocoetes. Mortality was less than IO/6 lor periods of 15 months

and metamorphosis occurred under these conditions' Rainbow trout (Salmo

ga,ird,ner.i Richardson) and goldfish (Carassius auratus Linnaeus) approxi-

mately 30 cm in length served as food sources for the parasitic species.

For histological preparations, lampreys were anaesthetized lightly in 2/6

ethyl urethane and fixed in Bouin's picro-acetic-formalin. Individuals less

than 140 mm in length were fixed in toto, the body wall being slit to permit

ready access of the fixative to the viscera. The digestive tracts of larger spe-

cimens were removed and fixed in small segments. The material was embedded

in Tissuemat of melting point 60-62"C, and sectioned at 7 p. Sections were

prepared through representative levels of the alimentary canal' mounted

serially, stained with Ehrlich's alum haematoxylin using Triosin as a coun-

terstain, and with Mallory's Triple Stain.

The course of the spiral valve of the mid-gut was reconstructed from gross

transverse sections of the tract cut at intervals of five somites.

The relative secretory-absorptive surface of the anterior mid-gut of am-

mocoetes and adults was estimated from transverse sections, by determining

the ratio of the linear measurement of the mucosal epithelium bordering the'lumen to the circumference at'the serosa' Microscopical preparations of the

mid-gut immediately posterior to the l iver were projected at a magnification

of 200 diameters and measurements were made by means of a map measure

with a revolution counter. The ratio of internal surface to circumference has

been termed the I/C ratio.

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BATTLE AND HAVASHIDA: LAMPREY ALIMENTARY TRACT 29I

MACROSCOPIC ANATOMY OF THE ALIMENTARY CANAL

AlruocoBrB

From the standpoint of gross structure, the alimentary tracts of thethree species of ammocoetes examined, namely, P. marinus, E. lamotten,ii,and 1. fossor, are almost identical (Fig. 1). The mouth overhung by the oralhood leads to a buccal cavity which is bounded posteriorly by a flap-like

AMG

PMG

Ftc. 1. Dorsal view of the intraperitoneal alimentary canal of P.morinus; 120-mm ammocoete on the left and 170-mm adult on theright. AMG, anterior mid-gut; H, heart; HG, hind-gut; L, l iver;

OE, metabranchial oesophagus; PMG, posterior mid-gut.

velum composed of right and left halves guarding the entrance to the tubularpharynx. Just caudad to the seventh pair of gill pouches at the level of theheart the pharynx merges dorsal ly into the narrow tubular metabranchial

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292 JoURN\L FISHITRIES I{ltsEARcII IioARD oF CANADA, YoL. 22' No' 2' 196s

oesophagus (Sterba, 1962) or fore-gut. The conical ventricle of the heart is

completely encircled by the rounded anterior end of the single-lobed liver

which then tapers sharply to the right (Fig.2). A conspicuous greenish-colored

gall bladder is partially embedded in the anterior dorsal aspect of the liver.

The oesophagus adheres closely to the anterior third of the dorsal surface o{

the liver, while posteriorly it lies in a dorsal concavity of the latter. Somewhat

anterior to the caudal margin of the liver, the tract abruptly dilates to approx-

imately three times the diameter of the oesophagus (Fig. 1, 2) and receives

the bile duct on its left margin, thus marking the anteriof end of the mid-gut

or intestine. The mid-gut progressively decreases in diameter to within a short

OE

LBD

AMG

Fro. 2. Ventral aspect of the alimentary canal of am-mocoete of. P. marinus (160 mm) showing oesophaglsmerging into anterior mid-gut with liver displaced to th.er ighi . AMG, anter ior mid-gut ; BD, b i le duct ; GB, gal l

bladder; 1,, liver; OE, oesophagus.

distance of the anus where it passes without gross demarcation into a short

hind-gut. Immediately anterior to the anus the hind-gut receives the prone-

phric ducts on either side and is now referred to as a cloaca (Fontaine, 1958).

Dorsal and ventral mesenteries are lacking except at the level of the hind-gut.

A broad mucosal fold, the spiral valve or typhlosole, extends into the

lumen of the mid-gut. It originates from the left wall of the anterior mid-gut

(Fig. a) and progressively decreases in height caudally, disappearing at thejunction of mid-gut and hind-gut. In both E. Iamotten|i, and L fossor its in-

sertion follows a straight course before undergoing a torsion to the mid-ventral

l ine along the posterior half to third of the mid-gut. In P. marinus the insertion

B

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tsATTLE AND HAYASHIDA: LAMPREY ALIMENTARY TRACT 293

anteriorly lies only slightly to the left of the mid-ventral line. It follows asomewhat irregular course between the mid-ventral and mid-left wall of thegut, exhibiting 2 or 3 torsions before passing along the mid-ventral wall. Daniel(1931) has referred to the expanded anterior portion of the intestine of theammocoete as the "median valvular intestine," and the tapering region the"post-valvular intestine." In the species described here the former wouldrefer to the complete mid-gut, the latter to the hind-gut.

RBcnNrr,v-MBreuonpnosBn Aour,r

The alimentary tracts of the adults of the four species of lamprey exhibitfundamentally the same anatomical relationships. The tract of P. rnar,inusremains functional for a period up to 2 years after metamorphosis (Applegate,1950) and decreases in diameter only on attainment of sexual maturity (Sur-face, 1899;Gage, 1928). Since E. Iamotten'i, i and 1. fossor cease to feed at met-amorphosis and the digestive tract is nonfunctional or commences to showdegenerative changes shortly after metamorphosis (Vladykov, 1949), thefollowing description is applicable to recently-metamorphosed individualsonly.

Immediately dorsal to the tongue at the posterior end of the buccal funnela srnall mouth leads into an enlarged buccal cavity, and thence into a narrow

AMG

Frc, 3. Dorsal view of alimentary tract of recently-meta-morphosed adult (160 mm) of P. mar'inus showing the diver-ticulum or caecum at the junction of oesophagus and mid-gut.AMG, anterior mid-sut;".3;n#;::,t."lum; [., liver; OE,

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294 JOURNAL I, 'ISIIERIES RESE.A.RcH BoARD oli CANADA, YoL. 22' No. 2' 1965

median tube, the epibranchial oesophagus, which arose during metamorphosis

by a lengthening of the larval gullet or metabranchial oesophagus dorsal to

the pharynx (Sterba, 1962). It continues as the metabranchial oesophagus

which occupies the mid-dorsal concavity of the anterior haif of the l iver' The

serosa along the right surface extends into a l igament passing to the dorsal

surface of the l iver. In both parasitic species, P. mardnus and 1. un'icuspis,

the left wall of the posterior end of the metabranchial oesophagus bears a

crescent-shaped thickening (Fig.3) which is an anteriorlydirected diverticulum

or intestinal caecum (Fontaine, 1958) of the mid-gut. No corresponding struc-

ture is present in the nonparasitic species. At the level of the posterior half

of the l iver the diameter of the gut increases to approximately three times that

of the oesophagus, marking the anterior end of the mid-gut. The mid-gut

gradually decreases in diameter as it passes posteriorly in the mid-ventral

coelom and merges imperceptibly into the short hind-gut. The cloaca does

not persist in transformed adults, the anus and urogenital papil la now opening

tiq

lii

i,i

A

d

P morinus | . unicuspis

A D

E. lomot ten i i

A D

l . f o s s o r

Frc. 4 Dragrammatic representation of the course of thg spiral valve of the mid-gut of ammo-

coetes and ai iu l ts of four species of lamprey. Cont inuous l ine. represents insert ion ot valve along

a;; ; ; l i l11 " i . t i - " . i . .v

c lnal : in terru i r t .a t in" represents ins6rt ioJr . a long ventra l hal f of a l i -

-eniuty ca"al. A, "-*6"o"te;

b, feedingadult; Cr, rirature migrant; D, recently-metamorphosed

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BATTLE AND HAVASHIDA: LAMPREY ALIMENTARY TRACT 295

independently (Fontaine, 1958). As in the ammocoete, dorsal and ventralmesenteries are lacking except at the level of the hind-gut.

The spiral valve of the mid-gut in adults (Fig. ) follows a more complexpathway than that of the ammocoete, presumably as a result of torsion anddifferential growth of the tract. In all four species the point of origin of thevalve is the right dorsal quadrant of the anterior mid-gut wall. It progressively

decreases in height as it follows a spiral pathway which is characteristic foreach species; and terminates its course in the mid-ventral wall a short distanceanterior to the hind-gut. In P. marinus the valve when viewed from the an-terior end follows a clockwise pathway for two complete revolutions; thenafter some rninor irregularity reverses its course for one and one-half revolu-tions. In I. uni,cuspis its course covers almost four clockwise revolutions.Although the two nonparasitic species do not feed as adults nevertheless thecourse of the spiral valve is more complex than in the ammocoete. In E. la-motten'i'i it executes one and one-half clockwise revolutions while in L fossorit follows a similar pattern except that the path becomes reversed midwayin the last half revolution.

The liver consisting of a single lobe appears reddish-orange in recently-metamorphosed individuals. Neither a gall bladder nor a bile duct is present,both having disappeared during metamorphosis as in Lampetra fl'uttiat'ilis(Krause, 1923; Sterba, 1962). The pancreas in lampreys is not present as adistinct organ, but is represented by patches of what are probably endocrinalacini within the wall of the anterior mid-gut adjacent to the l iver, and inparasitic species over the anterior margin of the diverticulum as well (Krause,1923 ; Roen ig ,1929 ; Ba r r i ng ton , 1945 ; Fon ta ine , 1958 ) .

MICROSCOPIC ANATOMY OF THE ALIMENTARY CANAI,

pnrnoayzo. MARrNUS

Parasitic species

Aulroconrn. The microscopic structure of the alimentary tract of theammocoete shows only minor variations over length ranges from 60 to 150 mm.

trn addition to the spiral valve which extends along the length of the mid-gut there are characteristic longitudinal mucosal folds or rugae. Three or fou,rhea.ry folds are present in the metabranchial oesophagus (Fig. 5) and five orsix in the hind-gut (Fig.6). The spiral valve of the mid-gut in sectional areaappears as a horseshoe-shaped typhlosole (Fig. 7) enclosing the large intestinalblood vessels.

The wall of the alimentary tract is composed of a mucosa consisting ofepithelium resting upon a basement membrane and a fibro-elastic connectivetissue Iamina propria, a connective tissue submucosa sometimes indistinguish-able from the latter, a tunica muscularis of circularly-arranged smooth musclefibres which form a complete layer only in the region of the hind-gut, and asercsa. The epithelial l ining along the course of the tract varies with respect

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296 Jour{NAL nISTIERIES RIISEARCH tsoARD oF- CANADA, \roL. 22, No. 2, 1965

to cell types and arrangements. The stratified cuboidal epithelium of the cen-tral oral cavity merges into a thin stratified squamous layer which lines mostof the pharynx, with the exception of the mid-dorsal and mid-ventral foldswhere ciliated simple columnar and pseudostratified types occur. Ciliatedpseudostratif ied columnar epithelium with numerous mucous cells forms thelining of the oesophagus (Fig. 8). Cil iated simple columnar epithelium coversthe typhlosole (Fig. 7) of the mid-gut as well as the opposing wall; pseudo-stratif ied columnar epithelium occurs in the lateral grooves or fornices. Theepithelium of the anterior hind-gut is cil iated simple columnar (Fig.6), andthat of the posterior hind-gut and cloaca stratified columnar which mergesinto stratified cuboidal epithelium continuous with the adjacent epidermis atthe anus. Three types of cells (Fig. 9) are present, tall columnar ones bearingcil ia, densely-staining serous or zymogenic cells, and lightly-staining mucouscells. The flask-shaped serous cells which are most abundant in the anteriormid-gut are laden with coarse acidophil ic granules. They correspond to thosedescribed by Brachet (1897) and by Krause (1923) for Lampetro. Barrington(1936) demonstrated their importance as a source of proteolytic enzymes.Vacuoles containing dense spherical basophil ic inclusions, resembling unicel-lular algae occur in the cells of both mid- and hind-gut (Fig. 10). Several speciesof unicellular algae, inclrrding Chlorogon'iurt sp. and Scenedesrnu.s sp., wereidentified in frozen sections of the alimentary canal, and in some instancesappeared to be in process of being engulfed by the epithelial cells. Throughoutthe entire gut, the epithelium exhibits active mitosis particularly in the for-nices. Spherical cells, 3-5 p in diameter, which occu,r among the epithelialcells appear to be migrant lymphocytes from the haemopoietic core of thetyphlosole (Fig. 9).

Ciliation of the tall columnar epithelia is present from the oesophagusto the hind-gut. Cilia (4-6 p) occur primarily in tracts over apical and lateralsurfaces of the typhlosole as described by Alcock (1899). In the fornices theapical surface of the cells resembles a thick brush border (l-2 p). Two regionscan be distinguished, an outer l ightly staining striated zone and an inner moredensely staining one. Electron micrographs (Fig. 11) indicate that the outerregion is made up of short cilia; and that the inner layer represents the rootletsof the same. The microvilli of the intestinal mucosa of Myrine, as describedby Adam (1963), lrear some superficial resemblance to these short cil ia, butthe latter in sectional area exhibit the characteristic arrangement of internallongitudinal filaments. Mitochondria occur below secretory vacuoles betweenthe rootlets.

The extra-epithelial trrnics are usually very thin and poorly developed.They are composed chiefly of collagenous fibres with relatively few elasticfibers and some smooth muscle. A lamina propria, when present at all, is

represented by a very few collagenous fibers immediately beneath the base-ment membrane. The tunica submucosa consists of an inner layer of highlyvascularized, loose fibro-elastic tissue, and a thicker moderately dense peri-pheral layer. The latter layer is thickest in the oesophagus and the hind-gut.

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BATI'LE AND HAYASHIDA: LAMPRIIY ALIMITNTARY 'IRACT 297

Areolar connective tissue containing the large intestinal blood vessels and anhaematopoietic centre comprises the core of the typhlosole. The circularlyarranged smooth muscle fibers are embedded within the outer margin of thesubmucosa. Oppel (1897) describes the muscularis as being composed of anouter longitudinal and an inner circular layer, with the latter being relativelythick in the hind-gut and very thin in both the oesophagus and the mid-gut.It has not been possible to establish the presence cf longitudinally arrangedsmooth muscle fibres in the ammocoete. The entire gut within the coelomiccavity is covered by a very thin layer of flattened mesothelial cells whichadheres to the smooth muscle by connective tissue fibres. This serosa appearsconsiderably thicker in the region of the hind-gut due to a transition from asquamous to cuboidal mesothelium, as well as an increase in the connectivetissue.

RBcBNrr,v-lrETAMoRpHosED ADULT. The alimentary tract undergoesconsiderable modification during metamorphosis especially with regard toincreasing complexity of the longitudinal mucosal folds. Low irregular foldsextend into the lumen of the epibranchial oesophagus and become moderatelytall as they are continued into the metabranchial oesophagus (Fig. t2),At the level of the anterior mid-gut, they increase in height and number,merging with those of the diverticulum. The posterior end of the oesophagusis marked on the right by the fusion of two folds which form the spiral valveof the anterior mid-gut. Alternating high and low longitudinal folds (40-85+)line the whole mid-gut including the surface of the spiral valve (Fig. 13).These folds progressively decrease in height posteriorly becoming few in num-ber and broad as they continue into the hind-gut (Fig. 1a).

The mucosa, submucosa, muscularis, and serosa comprising the wall ofthe gut show relatively few chang,es from those of the ammocoete. The extremeanterior end of the oesophagus is lined with stratified cuboidal epithelium,but pseudostratified columnar cells characterize the remainder of it. The epi-thelium of the mid-gut and the diverticulum is largely simple columnar exceptin the crypts where it becomes pseudostratif ied. In the anterior mid-gut, longcil ia occur in tracts over the folds, and short cil ia in the crypts. In the diver-ticulum, posterior mid-gut, and hind-gut, the arrangement is more irregular,where rvide bands of short cilia occur intermittently with narrower bands oflong cil ia, the latter always covering the tips of the folds. Mucous cells occurin the oesophageal epithelium, the diverticulum, the mid-gut, and hind-gutwhile serous cells with coarse acidophilic secretory granules are most abundantin the anterior mid-gut and diverticulum, but also extend as far as the hind-gut. Lymphocytes have impregnated the epithelium, even appearing withinthe cytoplasm, but cellular inclusions such as those occurring ir:r the ammo-coetes are not observed in any part of the tract.

FnBnrwc ADULT. The diameter of the entire tract has increased consid-erably over that of recently-metamorphosed individuals. Vladykov and Mu-kerji (1961) record a width of as much as 27 mm with an average of 9 mmimmediately posterior to the l iver, in actively feeding half-grown specimens.

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298 JOURNAL FISHERIES RESEARCH BOARD OF CANADA, VOL. 22, NO. 2, 1965

TesLB I. Ratio of internal surface to circumference (I/C)e for transverse sections of anteriormid-gut of lampreys at various stages.

Species Stage Length Sex I /C ratio

P. marinus

L unicuspis

E. lamottenii

I. Jossor

Ammocoete

Ammocoete

Post-metamorphosis

Feeding adult

Migrant adult

Spawning adult

Feeding adult

Spawning adult

Ammocoete

Ammocoete

Post-metamorphosis

Mature adul t

Ammocoete

Adul t

, m n

60

125

160

167

360

430

295

240

60

t17

160163

184163

135

L46

?

I

I

Io

6',

6 '

d

?

&d

o

1 . 2

1 . 3

, . J

t l . 4

6 . 9

5 . 6

1 0 . 6

4 . 5

1 . 1

1 . 2

3 . 3 b4 . 2 b

2 . 2 c1 .0d

1 . 1

o . 7

aData obtained from linear measurements of internal surface and circumference made by

il:fi$J:&#alrrneasure with a revolution counter on outline drawings (200 X) of histological

bMetamorphosed in April and May 1957 after 7 months in laboratory tanks.cAdult maintained in laboratorv tank Seotember and October 1957.dAdult maintained in laboratory tank Oitober to January 19.58.

The longitudinal mucosal folds of the oesophagus are taller and have becomelnore numerous. Those of the anterior mid-gut (Fig. 1.5) are fi lamentous andsometimes branched, while those of the posterior mid-gut (Fig. 16) are rela-tively unchanged. Due to a reduction in the connective tissue core, the typhlo-sole also appears filamentous and less bulbous.

The epithelium of the folds of the mid-gut and anterior hind-gut is simplecolumnar and that of the crypts is pseudostratif ied columnar. Many epithelialcells of the anterior mid-gut show evidence of being serous secretory (Fig. 17)'but mucous cells are also present. Masses of partially digested connectivetissue and muscle together with numerous nucleated erythrocytes in variousstages of cytolysis are present in the lumen of the anterior mid-gut (Fig. 15).The large numbers of serous cells would seeln to indicate that the anterior

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BATTLIT AND LIAYI\SHIDA: LANIPREY ALII\IENTARY 'l 'RACI'f 299

mid-gut and diverticulum of the adult are of primary importance in digestion

as in the ammocoete (Barrington, 1936). The apices of many cells of the pos-

terior mid-gut (Fig. 18) are translucent and their reaction with Mallory'sTriple Stain identifies them as mucous secreting. Long cilia form a dense cov-ering on the apices of the folds (Fig. 17), although in the posterior mid-gut andanterior hind-gut tracts of short cil ia predominate elsewhere.

Marunn MIGRANT ADULT. Applegate (1950) described a decrease in the

diameter of the alimentary tract consequent upon cessation of active feeding.

Initially the tract becomes flattened dorso-ventrally at the level of the liver.

Its histological structure is almost identical to that of a feeding individual

with the exception of the longitudinal folds of the anterior mid-gut (Fig. 19)

which now appear more tortuous. Some ernsion is occurring at the tips of thefolds. The contour of the typhlosole is not uniform throughout the mid-gut

since its attachment to the wall is intermittently broad and fi lamentous'

Cytolytic changes have been init iated in the epithelium of the whole mid-gut.

Extensive vacuolation is occurring immediately peripheral to the nuclei (Fig.

20). Many cells show c1'toplasmic inclusions which appear to be identical to

those present in the ammocoetes and could represent algae inadvertentlyingested during migration. The composition and arrangement of the extra-

epithelial tunics are similar to those of the recently-metamorphosed and feed-

ing individuals except that they are thicker and denser consequent upon a

tonic contraction of the musculature. The haematopoietic t issue now forms

a broad band in the submucosa of the whole mid-gut, but is less evident in

the typhlosole.SpawNtNc ADULT. Vladykov and Mukerii (1961) recorded a gut width

of only 1.5-3 mm for spawning individuals. The main histological changefrom that of the mature migrant occurs in the mucosa. The longitudinal foldsare showing an advanced degree of erosion (Fis. 21). The epithelium especiallyin the anterior mid-gut has decreased in height (Fis.22). The nuclei have mi-grated toward the free surface of the cells, the chromatin is less basophil icthan at any other stage, and the cytoplasm is almost completely vacuolated.These changes are similar to the atrophy described by Vasil ieva (1961) forthe spring Lampetra fl,uvi,atil'is consequent upon prolonged physiological fasting.

f c u r u v o tt v zol' urrcu.tPrs

FBnorNc ADULT. The mucosa of the alimentary tract of this species, asin P. rnarinezs, is thrown into numerous longitudinal mucosal folds. Those ofthe oesophagus (Fig. 23) are somewhat less prominent than in P. marinus.In the mid-gut alternate tall and low mucosal folds (60-80) are compactlyarranged and occasionally are forked at their free tips (Fig. 2a). The epitheliallining of the tract appears to be identical with that ol P. mar'inas with a singleexception: at the posterior level of the metabranchial oesophagus, the epithe-lium is a heavy noncil iated, stratif ied columnar type (Fig.23). Serous secre-tory cells with coarse acidophil ic granules are abundant throughout the diver-ticulum and mid-gut (Fig. 25).

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The extra-epithelial tunics are comparable to those of P. marinus exceptthat the tunica muscularis is more prominent although it also is incompleteexcept for the heavy circularis of the hind-gut.

SpawNrNc ADULT. The spawning adult unlike that of P. rnarinus showsrelatively little erosion of the longitudinal folds at any level of the tract (Fig.26). However, cytolysis of the epithelium (Fig. 27) is advanced as indicatedby excessive cytoplasmic vacuolation and migration of the nuclei toward theapical surface. Lymphocytes usually present only toward the bases of theepithelial cells are scattered throughout the cytoplasm.

Nonparasitic Species

Eurosp u nm u s LAMITTEN r r

Atr,tiuocoBrB. From the histological standpoint the alimentary tracts ofthe ammocoetes of E. l,amotten'ii ranging from 60 to 200 mm in length closelyresemble those of the sea lamprey.

RBcBNrr,v-lrETAMoRpHosED ADULT. The adult in this species is nonfeed-ing (Vladykov, 1949; Trautman, t957). The following description is basedon a male examined in April. The anterior epibranchial oesophagus is flatteneddorso-ventrally and its lumen is not patent. At the mid level, narrow longitu-dinal mucosal folds are present (Fig.28).The typhlosole of the anterior mid-gutis large and broadly inserted on the wall; longitudinal folds on both the ty-phlosole and the gut wall are low, blunt, and less in number (20-40) than inP. mar'inus (Fig.29). The latter folds almost disappear posterior to the l iverwhere the gut has retained the character of the ammocoete. They reappearin the posterior mid-gut as irregular projections, some 12 or more in number.The hind-gut (Fig.39) in all respects resembles that of P. marinus. The epi-thelium including ciliation and the extra-epithelial tunics of the tract aresimilar to those of the adult sea lamprev. Inclusions, which resemble speciesof algae occurring within the lumen of the gut, are present in the apices of theepithelial cells of the hind-gut.

PnocnnssrvE ATRopHrr oF Tr{E ALTMENTARv rRACT oF THE ADULT. Atrophyof the alimentary tract was followed throughout the winter in specimenscollected in September and maintained in laboratory aquaria. Those examinedin October, November, and December were males (155-185 mm in length),all with markedly enlarged testicular follicles; those in January, February,and March were females (145-165 mm in length) with ovaries containingmasses of well-developed oiicytes.

The tract of the October specimen is similar to that of the April one exceptat the'level of the hind-gut (Fig. 30). The entire epithelium is necrotic andthe larnina propria and submucosa are heavily infiltrated with lymphocytes,while the tunica muscularis appears to be intact (Fig. 31). The lumen is occu-pied by a fibrous coagulum composed of necrotic epithelium and lymphocytes.More extensive degeneration of the lining of the tract is apparent in the No-vember specimen. The oesophageal folds have become reduced in height (Fig.

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Bi\T'lLll .\ND IIAYASHIDT\: I.AMPRFiY ALTNIEN'I'AI{Y TRACT 301

32), and the lumen of the anterior mid-gut (Fig.33,34) is completely obliter-ated bv a massive accumulation of lymphocytes and necrotic epithelium.Necrosis is spreading to the connective tissue coats and muscularis throughoutthe whole mid-gut. The lumen of the posterior hind-gut is now completelyobstructed by a dense coagulum (Fig. 35) but necrosis has not yet involvedthe complgte muscularis. In the December specimen atrophy has extendedanteriorly to include the oesophageal mucosal folds, and peripherally to thetunica muscularis (Fig. 36).

The lumen of the oesophagus of the January specimen (Fig. 37) is oblit-erated throughout its entire length by a coagulum of necrotic cells and lym-phocytes; only the submucosa at the base of the folds and the muscularisappear to be intact. The epithelium of the typhlosole of the anterior mid-gutas well as the adjacent crypts is now low columnar, and necrosis is evidenton the opposing wall (Fig.38). The extra-epithelial tunics of the whole tractparticularly in the mid-gut and hind-gut (Fig. 39) are heavily infiltrated withlymphocytes, so much so that the submucosa actually appears to be increasedin thickness. In the February specimen, longitudinal mucosal folds throughoutthe tract have been eroded, although there is a remnant of the typhlosole inthe posterior mid-gut. The lumina of both mid-gut and hind-gut (Fig. 40)are now completely obliterated by coagula of necrotic t issue; and the ventralsurface of the mid-gut is fused with the l iver (Fig.41). The extra-epithelialtunics are reduced to a ferv collagenous and muscle fibers, infiltrated with lym-phocytes which have also penetrated the l iver parenchyma. The wall of themid-gut of the March specimen is very thin and now almost indistinguishablyfused with the l iver, which in turn is considerably smaller than in the Februaryspecimen.

Apparently necrosis of the tract in E. lamotlenii may commence eitherin the oesophagus or the hind-gut and correspondingly proceed posteriorly oranteriorly. There is no indication of coincident involvement of the liver inmale specimens examined in October, November, and December; whereas infemales in February and March the degenerating mid-gut wall is fused withthe liver.

Icuruvouvzonr' rosson

AunocoBrB. The alimentary tracts of atrrmocoetes of L fossor varyingin length from 100 to 135 mm are almost identical to those of P. mar,i,nus andE.lamotteni.i..

RBcBNrr-v-MErAMoRprrosE,D ADULT. Leach (1940) noted that at the onsetof transforrnation, the intestine ol L fossor is reduced in diameter, containsno food, and resembles a flatterted cord. He also found the oesophagus to bea closed collapsed tube posterior to the 2nd or 3rd gil l opening. In the speci-mens described here the lumen of the anterior end of the epibranchial oeso-phagus is intermittently occluded, and at such levels appears as a solid massof epithelial cells (Fig. 42). The posterior oesophagus (epibranchial and meta-branchial) has a small lumen and is lined with pseudostratified columnar

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epithelium (Fig. a3). Whereas longitudinal rnucosal folds characterize the mid-gut of the other three species, only the spiral valve is present in I. fossor. Itis broadly attached to the wall of the gut and hence in section the typhlosoleappears wedged-shaped rather than flask-shaped (Fig. a ). The epithelium issimple low columnar to cuboidal and the extra-epithelial coats are present butreduced in comparison to the parasitic species.

PnocnnssrvE ATRopHlr oF THE ALIMENTARy rRACT oF THE elulr. Thealimentary tract of a female specimen in February differed from that of therecently metamorphosed adult in that the diameter of the tract has decreased(Fig. a5). This decrease is not accompanied by a massive invasion of lympho-cytes as in E. larnotteni,i. It appears to be largely due to autolysis of some cells,since there is no obvious interference with the continuity of the epithelialsurface. The typhlosole has become flatter and less prominent, and the extra-epithelial tunics are reduced in thickness (Fig. a5). The lumen of the oesopha-gus of a fernale specimen examined in April is cornpletely obliterated by asolid mass of epithelial cells (Fig. a6). The now narrower lumen of the mid-gut (Fig. 47) is l ined by simple cuboidal epithelium. There is no evidence thatlymphocytes assulrre a major phagocytic role in the reduction of either theepithelium or of the extra-epitheliai tunics, since there is no rnarked increasein their numbers,

RELATIVE MUCOSAL EPITHELIAI, SURFACES OF- THE ANTEITIOR MID-GUTOF PARASITIC AND NONPARASITIC SPECItrS

A comparison of the relative secretory-absorptive area of the anterior mid-gut of the four species was made hy determining the ratio of the l ining epitheliumto the circumference of the tract (I/C ratio) from typical prepared transversesections. The results are given in Table I. In the three species examined theI/C ratio for ammocoetes is over the range 1.1-1.3. In both parasitic species,P. rnar' i,nus and 1. un'icu.sp'is, the internal surface is greatly increased in re-

cently-me{amorphosed individuals and reaches a peak in the feeding adult(I/C ratio of 11.4 for P. mar'inus). The ratio subsequently declines duringmigration and spawning when the tract is no longer functional and atrophyis init iated.

Irr the uonparasitic species E. lamotten'ii, even though the adult is non-

feeding, the epithelial surface of the recen,tly-metamorphosed individuals may

be trebled or almost quadrupled (I/C ratio of 3.3 and 4.2),but shows a declinein mature adults as necrosis sets in. In the I.fossor adult, where init ial atrophyis largely due to autolysis of some of the epithelial cells, the I/C ratio is ac-tual ly less (0.7) than that of the ammocoete (1.1) .

DISCUSSION

From both the macroscopic and microscopic standpoints the anatomy of

the alimentary canal of ammocoetes and adults of the nonparasitic and para-

sitic species are in general similar, but do exhibit certain differences. The adults

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]JATTLE AND HAYASHIDA: I.AMPREY ALIN{ENTARY TRACT

of the parasitic species possess a diverticulum or caecum of the anterior mid-gut. Krause (1923) and Barrington (1945) observed a similar structur.e inadults of. Lampetra fluviatilis and Maskell (1931) noted the presence of twotemporary diverticula in the ammocoetes of the genus Geotrio in New Zealand,Australia, and South America. Barrington (1945) suggested that these caecamay demonstrate the tendency of the secretory epithelium to form an out-growth fore-shadowing the pancreas of higher vertebrates. This would seemsignificant in view of the fact that acini, probably endocrinal ones of the pan-creas, do surround the anterior end of the diverticulum. It might be postu-lated that the caecum provides for increased secretory epithelium and absorp-tive area of the a"nterior mid-gut.

In the adult the extent of the internal secretory and absorptive surfaceof the alimentary canal is related to the life habits. The mid-gut of adultsof the parasitic species has an extensive internal surface area due to the de-velopment at metamorphosis of 40-85 longitudinal mucosal folds over thewhole wall including the typhlosole. Although the nonparasitic species do notfeed as adults, 20-40 low folds do arise in E. lamottenii and persist for a shorttime after metamorphosis. The mid-gut of L fossor resembles that of theammocoete with a spiral valve as the only internally directed fold. Thus theabsence of mucosal folds in the mid-gut of I. fossor and their presence in E.lamottenii suggest that the latter is less primitive than the former, substan-tiating a concept put forward by Hubbs (1924).

At the commencement of the spawning migration, parasitic forms ceaseto feed, whereas nonparasitic species do not feed after metamorphosis (Vla-dykov, 1949).In both biotypes cessation of feeding is accompanied by degen-erative changes. In P. marinus and I. unicuspis, the initial changes involvea progressive decrease in thickness of the epithelial lining of the tract, asnoted by Applegate (1950) for the former species. Vacuolation of the cellsoccurs together with a migration of the nuclei toward the free surface compar-able to that described by Vasilieva (1961) for Lampetra f,uaiatilis. This isaccompanied by lymphocyte invasion of the whole epithelial layer. Coincidentchanges involve contraction of the wall of the entire tract, and in P. marinusa degeneration of the apices of the longitudinal folds and ultimately of theentire folds. Atrophy of the tract differs in the two nonparasitic species E.lamottenii and ,I. fossor. That of E. lamottenai involves necrosis of the liningepithelium spreading peripherally, and accompanied by a massive invasionof lymphocytes. It may be init iated in either the oesophagus or hind-gut;that in L fossor is brought about initially by autolysis of some epithelial cellsthus reducing and ultimately obliterating the lumen of the tract without lossin continuity of the epithelial surface.

Algae as food for ammocoetes have been recorded by Creaser and Hann(.1929). Inclusions, presumably of algae occurred predominantly in the pos-terior mid-gut and to a lesser extent in the hind-gut of the four species. Similarinclusions were found in some adults of all species. Mathers (1926) howeverfound no trace of algae in the gut of ad,ult Entosphenus triilentalus, a parasitic

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301 .IOURNAL I. 'ISHERIES RESEAI{CH BOARD OF' CANADA, VQL. 22, NO. 2, 196.5

species. Such inclusions in the adult are diff icult to interpret, since it seemsunlikelv that algae would serve as a nutrielt source in parasitic forms.

ACKNOWLEDGMENTS

The authors are grateful to Drs W.A. Kennedy and J.J. Tibbles and MrA.H. Lawrie of the Fisheries Research Board of Canada Biological Station,London, Ontario, for collections of material, and for their interest and assis-tance at all t imes; to Dr D.A. Mclarty, Department of Rotany;, Universityof Western Ontario, for the identif ication of algae;to Mr C.E. Jarvis, Depart-ment of Microscopic Anatomy, University of Western Ontario, for preparationof photomicrographs; to Dr L. Threadgold, Queen's University, Belfast, North-ern Ireland, for an electron micrograph; and to Mrs M. Moulton and Mr A.Gage, Department of Zoology, Universit.-v of Western Ontario, for assistancein photography.

. REFERENCES

Ao-r.u, H. 1963, Structure and histochemistry of the alimentary canal, pp.256-288. In A.Brodal and R. Fdnge [Ed.] The biology of Myxine, Chap. 5. Universitetsforlaget, Oslo,Norway.

Arcocr, R. 1899. On proteid digestion in ammocoetes. J. Anat, Physiol. ,33: 612-637.Arrrncerr, V.C. 1950. Natural history of the sea lamprey (Petromyr.on marinus) in Michi-

gan. U.S. Fish Wil,d.l.iJe Sera., Spec. Sci. Rept., F,isheries, No. 55, pp. l-236.B.r.nnrNcroN, E.J,W. L936. Proteolytic digestion and the problem of the pancreas in ammo-

coete larva of Lampetra pl.aneri. Proc. Roy. Soc. Lond.on, Ser. B, 121:22I-232.1945. The supposed pancreatic organs of Petromyzon fl,uviatilis and Myxine glutinosa.

Quart. J. Micr. Sci., 85:39I-417.BoeNrc, H. 1929. Morphologie und Entwicklung der Pankreas beim Bachneunauge, III Teil,

Die Histologie und Histogenese des Pankreas. Z. Mikrosk. Anat. Forsch., 17: 125-184.Bnecnrt, A. 1897. Ddveloppement du pancrdas et du foie. J. Anat. Physiol. (Paris),32:

620-631.Cnn.tsnn, C., exo C.S. HeNw. 1929. The food of larval lamprey. Popers Mich. Acad. Sci.,

L0: 433-437.DeNror, F.J. 1931. Features in the development of ammocoetes. Univ. CaliJ. Publ'. Zool.,

3 7 ( 4 ) : 4 1 - 5 2 .FoNreri*r, M. 1958. Formes actuelles, super-ordres des Petromyzonoidea et des Myxinoidea.

Tome XIII Traitd de Zoologie (Pierre-P. Grassd), pp. 13-172. Masson, Paris.Gr.ce, S.H. 1928. The lampreys of New York State. Life history and economics. A biological

survey of the Oswego River system. Supp. to 17th Annual Report, State of NewYork Con-servation Department, pp. 156-191. 1927.

Hunns, C.L. 1924. The life-cycle and growth of lampreys. Papers Mich. Acad'. Sci., 4:587-603.

Kneuso, R. L923. Mikroskopische Anatomie der Wirbeltiere in Einzeldarstellungen. IVTeleostier, Plagiostomen, Zyklostomen und Leptokardier. Walter de Gruyter & Co. Berlinand Leipzig. Pages 764-858.

LlwzrNc, W.J.R. 1959. Studies on the river lamprey, Lampetra fluaiatilis, during its anadro-mous migration. Vitgeversmaatschappij Neerlandia-Utrecht, 82 pp.

Ln.lcu, W.J.- 1940. Occurrence and life hiitory of the northern brook lamprey, IchthyomyzonJossor it Indiana. Capeia, l(194941):21-34.

Mesrnr,r,, F.G. 1931. On the New Zealand lamprey, Geotria australis Gray. Part III. Theloss of the mid-gut diverticula of the ammoco-etei stage at metamorphosis. Trans. Proc.New Zealand. Inst,,62: 120-129,

M.r,rnens, V.C. 1926. The velar apparatus of Entosphenus trid,entatus. Anat. Rec,,.34: _55-p0.Orrer, A. t896, 1897. Lehrbuch- der Vergleichenden Microskopischen Anatomie. Verlag

von Gustav Fischer. Jena. Vols. I, II.Sronee,, G. 1962. Die l,Ieunaugen (Petromyzonidae) Band III Handbuch der Binnenfischerei

Mitteleuropas. E. Schweizeibart 'sche Verlagsbuchhandlung. Stuttgart. Pages 263-352'.SuHFe,ce, H.A.- 1899. Removal of lamprey from the interior waters of New York. 4Lh Ann.

Rept., N.Y. Comm; Fish. Game aniJ Forests, pp. I9l-245.Tna.urrrrafr, M.B. t957. The fishes of Ohio. The Ohio State Univ. Press, Columbus. Pages

131-1 .50 .

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I}-A.TTLE AND HAY.\SHIDA: LAMPREY ALIMENTARY TRACT

Vesnreve, N.!'. 1961. Functional variability of intestinal epithelium in Baltic lamprey,Lampetra f uoiatilis L. Arkh. Anat. Gi,stol,. i,. Embriol , al (11) : 96-100.

Vr*rovrov, V.D. 19+9. Quebec lampreys (Petromyzonidae). I. List of species and their eco-nomic importance. Conlrib. Quebec Dept. oJ Fish., No. 26, pp. t-67.

1950. Larvae of eastern American lampreys (Petromyzonidae). 1. Species with twodorsal fins. Nat. Canadien, 77 (3-4) : 73-95.

1960. Description of young ammocoetes belonging to two species of lampreys Petro-myzon marinus and Entosphenus l,amotlenii. J. Fish. Res. Bd.. Canada, L7 (2) : 267-288.

VraoYr<ov, V.D., eNl G.N. Mur<nnyL 1967. Order of succession of different types of infra-oral lamina in landlocked sea lamprey (Pelromyzon marinus). J, Fish. Res. Bd. Canada,I B ( 6 ) : 1 1 2 5 - 1 1 4 3 .

E x p r a w a r r o N o F F I G U R E SPlate I

Frc. 5-10. Photomicrographs of histological cross sections of the alimentary canal of the am-mocoete of P. marintts (i25 mm). All sections 7p in thickness and stained with Ehrlich's alumhaematoxylin and Triosin. CE, simple columnar epithelium; I, inclusion; L, lymphocyte; LC,long c i l ia ; LP, lamina propr ia; M, mi tochondr ia; N{C, mucous cel l ; PE, pseudostrat i { ied columnarepi thel ium; R, root let ; S, serosa; SC, shor i c i l ia ;SER, serous cel l ;SM,.submucosa;SV, secretory

vacuole; T, typhlosole (spiral valve); TM, tunica muscularis.Frc. .5. Metabranchial oesophagus at level of the heart showing mucosal

folds bearing long cilia.Frc. 6. Anterior hind-gut lined with simple columnar epithelium.

Frc. 7. Anterior mid-gut s.howing horseshoe-shaped typhlosole with hae-matoDoretrc connectrve tlssue core.

Frc. 8. Ciliated pseudostratified columnar epithelium of oesophagus.Ftc. 9. Ciliated pseudostratified columnar epithelium of anterior mid-gut.

Frc. 10. Epithelium of mid-gut showing basophilic inclusions.Ftc. 11. Electron micrograph of apical area of epithelial cell of mid-gut

showing short c i l ia .

Plate II

Frc. 12-20. Photomicrographs of histological cross sections of the alimentary canal of adultP. marinus. All sections 7p in thickness and stained with Ehrlich's alum haematoxvlin and Trio-s i n . D , d i ve r t i cu l um;F , f oo l mass : [ , i n c l us i ons ; LC , l ongc i l i a : LP , l am ina p rop r i a l MC, *ucouscell; OE, oesophagus (metabranchial); P, pancreatic tissue; SCE, stratified columnar epithelium;SER, serous ie l l ; -SM, submucosa; T, typhlosole (spira l valve); TM, tunica musculai is ; V, va-cuole. (Fig. 12-14, recent ly-metamorphosed indiv idual (157 mm); Fig. 15-18, feeding adul t

(167 mm); Fig. 19-20, mature migrant (360 mm).)Ftc. 12. Section showing metabranchial oesophagus with low irregular

mucosal folds on the right, diverticulum on the left.Ftc. 13. Anterior mid-gut showing alternating ta1l and low mucusal folds.

Frc. 14. Hind-gut show-ing few heavy mucosal folds.Frc. 15. Anterior mid-gut showing alternating tall filamentous and low

Frc . 16 .

Frc . 17 .

mucosal folds.Posterior mid-gut showing fewer and heavier mucosal folds than

in anterior hind-gut.Pseudostratified columnar ciliated epithelium over lateral surface

of fo ld, anter ior mid-gut .

JIJ.)

Ftc. 18. Pseudostratified columnar ciliated eoithelium. of fold, Dosteriormid-gut . Apices of cel ls show muious secret ion.

Fro. 19. Anterior mid-eut showing tortuous tall mucosal folds.Frc. 20. Pseudostrat i f ied col imnar eoi ihel ium of anter ior mid-eut show-ing algal- l ike inc lusion and in i t iat ion of vacuolal ion of cel ls per- ipheral to

nucle i .

Plate III

Ftc.2l'27. Photomicrographs of histological cross sections of the alimentary canal of P.marinus and. I. unicuspls. A11 sections 7p in thickness and stained with Ehrlich's alum haematox-ylin and Triosin. C, cilia; D, diverticulum; EF, eroded mucosal fold; I., lymphocyte; LI, liver;T, P, lamina propr ia; N, nucleus;OE, oesophagus (metabranchial ) ; SER, serous cel l ;T, typhlosole(spira l fo ld) ; V, vacuole. (Fig.21,22, spawning adul t (350 mm) of P. mar inusi Fig. 23-25, feeding

adu l t o f Lun i cusp , i s ( 290mm) ;F ig .26 ,27 , spawn ingadu l t o f I . un i cusp i s ( 280mm) . )Frc.21. Anterior mid-gut showing extensive erosion of both tall and low

mucosal folds.

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Low columnar epithelium of anterior mid-gut showing nucleibecoming less basophilic, and vacuolation of cytoplasm.Section at posterior end of oesophagus (metabranchial) at level

of diverticulum.Frc. 24. Anterior mid-gut showing alternating tall and low mucosal folds.Ftc. 25. Mucosal fold showing densely basophilic nuclei and serous secre-

tory cells.Frc.26. Anterior mid-gui showing intact mucosal folds.

Frc. 27. Pseudostratified c^lumnar epithelium of anterior mid-gut show-ing nuclei migrating to free surface, lymphocyte invasion, and vacuolation

of cytoplasm.

Plate IV

Frc. 28-36. Photomicrographs of histological cross sections of the alimentary canal of adult(male) E. lamottenii. All sections 7 p in thickness and stained with Ehrlich's alum haematoxylinand Triosin. L, lymphocyte; LI, liver; LP, lamina propria; NT, necrotic tissue; SM, submucosa;T, typhlosole; TM, tunica muscular is . (Fig.28,29, recent ly-metamorphosed indiv idual (160mmI;-Fig.30,31, October adul t (185 mm); Fig.32,33,34,35, November adul t (154 mm); Fig.

36, December adul t (184 mm).)Frc. 28. Oesophagus with narrow elongated mucosal folds.

Frc. 29 Anterior mid-gut with low mucosal folds.Frc. 30,31. Hind-gut showing necrosis of whole epithelial lining and heavy

infiltration of lymphocytes into lamina propria and submucosa.Frc. 32. Oesophagus with some reduction of mucosal folds.

Frc. 33,34. Anterior mid-gut with lumen completely obliterated by necroticepithelial tissue and masses of lymphocytes. Necrosis has extended to extra-

eoi thel ia l tunics.Frc. 35. Hind-gut with lumen obstructed by necrotic tissue. Necrosis

extends into tunica muscularis.Frc. 36. Oesophagus showing complete erosion of mucosal folds and con-

nective tissue tunics but not muscularis.

Plate Y

Fro. 37-41. Photomicrographs of histological cross sections of the alimentary canal of adult(female) E. lamottenii. All sections 7 p in thickness and stained with Ehrlich's alum haematox-y l in and Tr iosin. (Fig.37-39, January adul t (163 mm);Fig.40-42, February adyl t (146 mm).)C, coagulum of necrotic tissue; EE, eroded epithelium; L, lymphocyte; LI, liver; SM, submucosa;-

O, ovum; T, typhlosole (spiral valve); TM, tunica muscularis.Frc. 37. Oesophagus with eroded mucosal folds, coagulum of necrotic tissue

obstructing lumen.Frc. 38. Anterior mid-gut showing some erosion of epithelium on wall

opposite typhlosole.Frc. 39. Hind-gut showing no erosion of epithelium but some invasion of

submucosa bv lvmohocvtes.Frc. 40. Hind-gut with mucosa cornptetlty necrotic. Lymphocytes have

invaded to margin of tunica muscularis.Frc. 41. Anterior mid-gut mucosa completely eroded, ventral surface ofmuscularis fused with liver, which also shows extensive invasion by lympho-

cYtes'

Plate VI

Frc. 4217. Photomicrographs of histological cross sections of the alimentary canal of adultI.fossor. All sections 7 p in thickness. Fig.42-44 stained with Mallory's Triple Stain; Fig.45-47with Ehrlich's alum haematoxylin and Triosin. MGL, mid-gut lumen; OE, oesophageal epithe-lium; O, ovum; PE, pseudostratified columnar epithelium; T, typhlosole (spiral valve). (Fig.4244, recent ly-metamorphosed indiv idual (146 mm);Fig,45, February adul t (155 mm); Fig.

46, 47, April adult (145 mm).)Frc. 42. Anterior end of epibranchial oesophagus showing lumen occluded

bv eoithelial cells.Frc. 43. Posterior end of epibranchial oesophagus lined by pseudostratified

columnar eoithelium.Frc. 4,1. Anterior mid-gut showing w'edge-shaped typhiosole (spiral valve).

Frc. 45. Anterior mid-gut with reduced lumen, flattened typhlosole.Frc. 46. Oesophagus (metabranchial) with lumen obliterated.

Frc. 47. Reduced anterior mid-gut with narrow lumen, typhlosole no longerevident: epithelium now cuboidal is still intact.

F r c . 2 2 .

Frc . 23 .

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