lectures on the organs of reproduction in the animal kingdom

2
268 9- lines, the proportion not being by any means so great as in the adult specimen; showing that the juvenile proportions of those parts remain, or even increase in the adult Gibbon : the reverse of man’s economy. LECTURES ON THE ORGANS OF REPRODUCTION IN THE ANIMAL KINGDOM. DELIVERED IN THE ROYAL COLLEGE OF SUR- GEONS, LONDON. By PROFESSOR OWEN, F.R.S. LECTURE V.-APRiL 30,1840. BESIDES the forms of generation already spoken of in the preceding lectures, some authors admit another kind, which they call gemmuliparous; they suppose the granules which are produced within the cavities of the polypi to be portions of the flesh of the animal, developed and separated from the internal membrane, and afterwards covered with cilia. There exists, however, no proof of this separation, and the researches of Wagner and Farre tend to disprove such supposition; the former physiologist has examined the ova at a very early period, and has found them enclosed in distinct ovisacs, and to contain all the essential parts of the ova of higher animals, viz., the vitellus, ger- minal sac, and germinal spot. We next proceed to a higher class, the RADIATA, beginning with the order Acalepha (sea nettles) in which are contained the medusae, the beroe, and the hydrostatic genera, as the physalia, &c. Our know- ledge of the modes of generation in this order are very restricted, and in one genus alone have been fully investigated, viz., in the Medusa; in the Physalia the reproduc- tive organs are situated in the midst of the numerous tentacula, which depend from the under part of its sac; in the beautiful little Velella, with its pigmy sail, raised upon an oval disk, these organs are found among the tentacula, which hang from the inferior surface of the disk ; they resemble tenta- cula in their form, and have been observed sometimes to contain a whitish, opake fluid, and sometimes ova. The nature of the re- productive organs in the medusa is now well known ; in the Rhizostoma, one of the com- monest species, four distinct openings will be seen upon the under surface of the dome of the animal, and near the base of the ten. tacula. These openings lead into four gene. rative sacs, guarded by a valve, and sepa- rated from the digestive cavity by a thin membrane only ; they have hitherto been described, by comparative anatomists, as reo spiratory cavities; the generative sacs may be easily seen through the transparent and jelly-like structure of the dome-shaped disk; and Ehrenberg has remarked upon the great variety of their disposition in different spe. cies; in some they are placed at-consider- able distances from each other, and in others they lengthen out until they become continu- ous ; the entrance to these sacs is provided with numerous small tentacles, upon which vibratile cilia are placed, which keep up a constant current of fresh sea-water through the cavity ; within the sac, when examined in the spring, is a riband-like membrane, which increases in size during the summer, and becomes plicated so as to present a stir- face of very considerable extent. The re- searches of Ehrenberg, Rudolph Wagner, and Siebold into the nature of these organs, has led to the discovery, that the Medusaeare dioecious ; that within this plicated mem- brane, in the males, are produced sperma- tozoa, and in the females true ova of a violet colour ; the spermatozoa are disposed within the membrane in a very remarkable manner; they are collected, lying parallel with each other, into small conical masses, each en. closed in a pyriform sac, the apex of the cone being formed by the terminations of their tails, and connected to the surface of the membrane. The mode of propagation in the Medusae must be the same as in bivalve mollusca and fishes; the generative fluid, with these spermatozoa, must bedispersed in the neighbourhood of the females, so as to impregnate the ova. Gader observed, that during the breeding season, the generative sacs were emptied of their ova, but that there existed numerous small marsupial bags of a pyriform shape appended to the fringes of the tentacula. These marsupia contain from four to six or eight ova in different de- grees of development, and are closed on all sides, so that when perfected, they escape into the surrounding medium by means of the rupture of the sac. In this curious dis- position we are reminded of the peculiar mode of generation of the marsupial mam- malia, and the transition of the ova from the generative sacs to these small marsupial bags is equally mysterious with the passage of the embryo from the uterus of the kanga- roo into the marsupial pouch. During this remarkable transit it is known that the ova lose all trace of the germinal sac and spot ; they become granular in their contents, and change their colour from violet to yellow; the spermatozoa are expelled from the plicated membrane of the generative sac in the form of a lengthened thread, the base of each

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Page 1: LECTURES ON THE ORGANS OF REPRODUCTION IN THE ANIMAL KINGDOM

268

9- lines, the proportion not being by anymeans so great as in the adult specimen;showing that the juvenile proportions ofthose parts remain, or even increase in theadult Gibbon : the reverse of man’s economy.

LECTURES

ON THE

ORGANS OF REPRODUCTION IN THEANIMAL KINGDOM.

DELIVERED IN THE ROYAL COLLEGE OF SUR-

GEONS, LONDON.

By PROFESSOR OWEN, F.R.S.

LECTURE V.-APRiL 30,1840.BESIDES the forms of generation already

spoken of in the preceding lectures, someauthors admit another kind, which they callgemmuliparous; they suppose the granuleswhich are produced within the cavities ofthe polypi to be portions of the flesh of theanimal, developed and separated from theinternal membrane, and afterwards coveredwith cilia. There exists, however, no proofof this separation, and the researches of

Wagner and Farre tend to disprove suchsupposition; the former physiologist has

examined the ova at a very early period, andhas found them enclosed in distinct ovisacs,and to contain all the essential parts of theova of higher animals, viz., the vitellus, ger-minal sac, and germinal spot.We next proceed to a higher class, the

RADIATA, beginning with the order Acalepha(sea nettles) in which are contained the

medusae, the beroe, and the hydrostaticgenera, as the physalia, &c. Our know-

ledge of the modes of generation in thisorder are very restricted, and in one genusalone have been fully investigated, viz., inthe Medusa; in the Physalia the reproduc-tive organs are situated in the midst of thenumerous tentacula, which depend from theunder part of its sac; in the beautiful littleVelella, with its pigmy sail, raised upon anoval disk, these organs are found amongthe tentacula, which hang from the inferiorsurface of the disk ; they resemble tenta-cula in their form, and have been observedsometimes to contain a whitish, opake fluid,and sometimes ova. The nature of the re-

productive organs in the medusa is now wellknown ; in the Rhizostoma, one of the com-monest species, four distinct openings willbe seen upon the under surface of the dome

of the animal, and near the base of the ten.tacula. These openings lead into four gene.rative sacs, guarded by a valve, and sepa-rated from the digestive cavity by a thinmembrane only ; they have hitherto been

described, by comparative anatomists, as reospiratory cavities; the generative sacs maybe easily seen through the transparent andjelly-like structure of the dome-shaped disk;and Ehrenberg has remarked upon the greatvariety of their disposition in different spe.cies; in some they are placed at-consider-able distances from each other, and in othersthey lengthen out until they become continu-ous ; the entrance to these sacs is providedwith numerous small tentacles, upon whichvibratile cilia are placed, which keep up aconstant current of fresh sea-water throughthe cavity ; within the sac, when examinedin the spring, is a riband-like membrane,which increases in size during the summer,and becomes plicated so as to present a stir-face of very considerable extent. The re-searches of Ehrenberg, Rudolph Wagner,and Siebold into the nature of these organs,has led to the discovery, that the Medusaearedioecious ; that within this plicated mem-brane, in the males, are produced sperma-tozoa, and in the females true ova of a violetcolour ; the spermatozoa are disposed withinthe membrane in a very remarkable manner;they are collected, lying parallel with eachother, into small conical masses, each en.closed in a pyriform sac, the apex of thecone being formed by the terminations oftheir tails, and connected to the surface ofthe membrane. The mode of propagation inthe Medusae must be the same as in bivalvemollusca and fishes; the generative fluid,with these spermatozoa, must bedispersed inthe neighbourhood of the females, so as toimpregnate the ova. Gader observed, thatduring the breeding season, the generativesacs were emptied of their ova, but thatthere existed numerous small marsupial bagsof a pyriform shape appended to the fringesof the tentacula. These marsupia containfrom four to six or eight ova in different de-grees of development, and are closed on allsides, so that when perfected, they escapeinto the surrounding medium by means ofthe rupture of the sac. In this curious dis-

position we are reminded of the peculiarmode of generation of the marsupial mam-malia, and the transition of the ova from thegenerative sacs to these small marsupialbags is equally mysterious with the passageof the embryo from the uterus of the kanga-roo into the marsupial pouch. During thisremarkable transit it is known that the ovalose all trace of the germinal sac and spot ;they become granular in their contents, andchange their colour from violet to yellow; thespermatozoa are expelled from the plicatedmembrane of the generative sac in the formof a lengthened thread, the base of each

Page 2: LECTURES ON THE ORGANS OF REPRODUCTION IN THE ANIMAL KINGDOM

269

pyriform sac being attached to the apex ofthe next.

Development of the Ova of 1Jledusae.-It isa question whether the ovum is at first pro-vided with an external membrane or chorion ;it is probable, from a consideration of thechanges which it subsequently undergoes,that such is not the case, but that this mem-brane becomes developed at a later period.In the first instance, Wagner has observed,that the ovum becomes slightly lengthened,and indented at a point which is constant,on one side ; this indentation gradually be-comes a cleft, which divides the ovum intotwo equal halves; other fissures are then

formed, which subdivide the ovum at firstinto four portions, then into numerous

smaller parts, and, eventually, into a greatnumber of minute granules; the vitellinegranules next assume a radiated form, leav-ing an unoccupied space in the centre, andat the same time an. external epithelium,furnished with cilia, is produced, and theovum commeices a rotatory movement. Thenext change that occurs, is an alteration incolour from violet to yellow, the assumptionof an elongated oval shape, and the forma-tion of a slight oral depression at their greatextremity. It is in this state that they quitthe marsupium, and here we are forcibly re-minded of the form and condition of thelower infusoria; in a short time a circularring begins to be seen around the oval extre-mity, and short processes, furnished withcilia, are produced from the ring, giving tothis stage of the development a close resem-blance to the rotiferous infusory. In thenext place, the processes developed aroundthe mouth become elongated into eight ten-tacuia, provided with cilia; the mouth com-municates with the internal intestinal canal,and the entire embryo has taken on the cha-racters of a polypus, feeding on infusory ani-malcules and minute forms of its own spe-cies. In this state it is probable that the

young mednsae sink to the bottom of the seain shallow situations, and bury themselvesin the mud aud sand during the winter sea-son, and either continue their growth there, orrise in the spring to complete their adult form.Siebold kept some of these embryos throughthe winter, but failed in procuring their

complete development, a circumstance whichcannot be wondered at, when it is recol-lected that the tadpole is unable to assumeits perfect condition in captivity.

In one genus of Acalepha, fixed gemma-tion takes place, the newly-formed gemmaeassuming the perfect form of the parent, butremaining connected with her and with eachother.ECHINODERMATA.-The echinodermata are

completely dioecions, possessing distinclmale and female organs, and losing altogethelthe power of non-sexual reproduction byfission and generation. In the Asterias, a ra.mified digestive sac, with two ramified gene.

rative organs, are contained in each ray,and open by two distinct foramina at itsbase; in the generative sacs of some indi-viduals a whitish granular substanceis foundinthe spring, and spermatozoa inthe summerand autumn ; in others, ova are discoveredin great numbers in the breeding season ;in the Encriizus and Comatula, the generativesacs are more subdivided, and present alower condition; they are situated in the

radiating arms ; in the Echini, the generativeorgans are attached to that portion of theinternal surface of the shell which is oppositeto the mouth ; in the echinus :esculentus,five lobulated sacs are placed around theanus, which are either ovaries or testes, ac-cording to the sex of the individual ; theyopen upon the exterior by means of pores inthe shell in this situation ; these pores aredistinctly seen in the fossil species. If wewere to suppose the shell of the echinus tobe softened, and the animal drawn out intoa vermiform figure, we should then have theorganisation of the worm-like Holothuria ; inthis genus the generative organ is a singlesystem of ramified tubes, opening near themouth of the creaÍ1ue; the remarkable coecalpouch connected with this apparatus, andwhich has hitherto been considered a rudi-mentary testis, has been proved, by the re-

cent careful observation of Rudolph Wag-ner, to contain no vestige of. spermatozoa atany period. It is probably intended to addsome substance to the ovum previously to itsexpulsion; in the Sipunculus there are twoorgans, which are neither ramified nor di-vided, and are, therefore, simpler than theramified organ of the holotburia ; it is prob-ably dio3cious,but new observations are re-quired to ascertain whether, in some indivi-

dnals, they may contain spermatozoa. Atthis very early stage of our inquiry into thecondition of the generative organs in thelower animals, we cannot but feel some de-

gree of astonishment in discovering distinctL sexes, organs of generation as complete asare to be found in many of the higher classes,and that remarkable process in the medusse

which assimilates them in their mode of re-

production with the marsupial mammifera.

PATHOLOGY OF THE BRAIN IN ANIDIOT FROM INFANCY.

To the Editor of THE LANCET.SIR-Will you oblige me by an insertion

of the subjoined case in the columns of yourvaluable periodical? I am, Sir, your obe.dient servant,

GEORGE LOWTHER, M.R.C.S.Kingston-upon-Hull,

April 25, 1840.

On the 27th of December, 1839, I wasrequested to attend Sarah Oliver Foster, agirl of delicate frame, tall in stature, aged

GEORGE LOWTHER, M.R.C.S.