REVIEW.

Lectures on the Elements of Comparative Anatomy. ByTHOMAS HENRY HUXLEY. London : Churchill & Sons.

THIS work consists substantially of the lectures deliveredby Professor Huxley in the spring of 1863, at the RoyalCollege of Surgeons of England, in discharge of his duties asHunterian Professor of Comparative Anatomy and Physiologyto the College. Although this work may be regarded asfragmentary, consisting, as it does in the first place, of sixlectures on the Classification of Animals, and eight lectureson the Vertebrate Skull, the author hopes eventually tobring out subsequently other courses of lectures, and thus toproduce a systematic work on Comparative Anatomy. Thosewho have in any manner regarded the publications of Pro-fessor Huxley, will be glad of the prospect of having pre-sented to them a systematic view of the opinions held by onewho has distinguished himself by his contributions to almostevery deB%ytment of zoological and physiological inquiry.Professor Huxley says, with regard to this work, that inintention therefore the present work is the first of a series,to be followed in due order by a second volume on " Manand the other Primates," and a third on the remainingMammalia^ and so on. As far as the inquiries with themicroscope are concerned, we must content ourselves withdrawing attention to those parts of the present volume whichare devoted to the classification of animals. We cannot pre-

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64 HUXLEY, ON CLASSIFICATION.

tend to follow Professor Huxley into those details which leadhim to differ with Professor Owen with regard to the theo-retical structure of the vertebrate skull. We can only say,with regard to this second part of his work, that it willafford to all students of comparative anatomy, an example ofhow great is the power of analysis demanded of, and how wideare the inquiries of, the philosophical anatomist. I t is only ina very subsidiary way that the minute inquiries of the micro-scopist can assist the anatomical .philosopher in arriving atthe general laws which regulate the morphology of the higherclasses of the animal kingdom.

It is in the lower forms of animal life that the zoologistmust have recourse to the microscope. Whole families andtribes of every division of Invertebrate animals can alone bedetected by the aid of the microscope, and it is by its aidalone that the comparative anatomist and zoologist havebeen enabled to group the various species into somethinglike harmonious relationship. I t would be almost impossiblefor us to criticise the various positions taken by ProfessorHuxley with regard to the classification of the lower animals.He has recast the groups formerly known so well as theRadiata, of Cuvier, and which embraced so large a fieldof inquiries open to the microscopisfc, and we lake advan-tage of the permission of the publishers to reproduce the firstlecture of this series entire.

THE GREGARINIDA, RHIZOPODA, SPONGIDA, ANDINFUSORIA.

BY the classification of any series of objects, ia meant the actual,or ideal, arrangement together of those which are like and theseparation of those -which are unlike; the purpose of this arrange-ment being to facilitate the operations of the mind in clearlyconceiving and retaining in the memory, the characters of theobjects in question.

Thus, there may be as many classifications of any series of natural,or of other, bodies, as they have properties or relations to oneanother, or to other things; or, again, as there are modes in whichthey may be regarded by the mind: so that, with respect to suchclassification as we are here concerned with, it might be more proper

HUXLEY, ON CLASSIFICATION. 65

to speak of a classification than of the classification of the animalkingdom.

The preparations in the galleries of the Museum of this Collegeare arranged upon the basis laid down by John Hunter, •whoseoriginal collection was intended to illustrate the modifications •whichthe great physiological apparatuses undergo in the animal series:the classification which he adopted is a classification by organs, and,as such, it is admirably adapted to the needs of the comparativephysiologist.

But the student of the geographical distribution of animals,regarding animated creatures, not as diverse modifications of thegreat physiological mechanism, but in relation to one another, toplants and to telluric conditions, would, with equal propriety, disposeof the contents of a Zoological Museum in a totally different manner;basing his classification, not upon organs, but on distributionalassemblages. And the pure paleontologist, looking at life from yetanother distinct point of view, would associate animal remainstogether on neither of these principles, but would group them accor-ding to the order of their succession in Time.

Again, that classification which I propose to discuss in the presentLectures, is different from all of these : it is meant to subserve thecomprehension and recollection of the facts of animal structure; and,as such, i t is based upon purely structural considerations, and maybe designated a Morphological Classification. I shall have to consideranimal?, not as physiological apparatuses merely; not as related toother forms of life and to climatal conditions; not as successivetenants of the earth; but as fabrics, each of which is built upon acertain plan.

It is possible and conceivable that every animal should have beenconstructed upon a plan of its own, having no resemblance whatsoeverto the plan of any other animal. For any reason we can discover tothe contrary, that combination of natural forces which we term Lifemight have resulted from, or been manifested by, a series of infinitelydiverse structures: nor, indeed, would anything in the nature of thecase lead us to suspect a community of organization between animalsso different in habit and in appearance as a porpoise and a gazelle,an eagle and a crocodile, or a butterfly and a lobster. Had animalsbeen thus independently organized, each working out its life by amechanism peculiar to itself, such a classification as that which isnow under contemplation would obviously be impossible; a morpho-logical, or structural, classification plainly implying morphological,or structural, resemblances in the things classified.

As a matter of fact, however, no such mutual independence ofanimal forms exists in nature. On the contrary, the different mem-

6 6 HUXLEY, ON CLASSIFICATION.

bers of the animal kingdom, from the highest to the lowest, aremarvellously interconnected. Every animal has a something incommon with all its fellows ; much,' with many of them; more; witha few; and, usually, so much with several, that it differs but littlefrom them. '

Now, a morphological classification is a statement of these grada-tions of likeness which are observable in animal structures, and itsobjects and uses are manifold. In the first place, it "strives to throwour knowledge of the facts which underlie, and are the cause of, thesitoilarities discerned into the fewest possible"general propositions—subordinated to one another, according to their greater or lessdegreeof genei'ality; and in this way it answers the purpose of' a memoriateohnica, without which the mind would be incompetent tograsp andretain the multifarious details of anatomical science.

But there is a second and even more important aspect of morpho-logical classification. Every group in that classification is such invirtue of certain structural characters, which are not only commonto the members of that group, but distinguish it from all others; andthe statement of these constitutes the definition of the' group.

Thus, among animals with vertebrae, the class Mammalia is de-finable as thoae which have two occipital condyles, with a well-ossifiedbasi-occipital; which have each ramus of the mandible Composed ofa single piece of bone and articulated with the squamosal" element ofthe'skull; and which possess maminee and non-nucleated red blood-

But this statement of the characters of the class Mammalia issomething more than an arbitrary definition. I t does not merelymean that naturalists agree to call such and such animals Mann/malia;but it expresses, firstly, a generalization based upon, and constantlyverified by, very wide experience; and, secondly, a belief arising outpf that generalization. The generalization is that, in nature, thestructures mentioned are always found associated together: thebelief is, that they always have been, and always will be, found soassociated. In other words, the definition of the class Mcvmnalia isa statement of a law of correlation, or coexistence, of animal struc-tures, from which the most important conclusions are deducible.

For example: if a fragmentary fossil be discovered^ consisting ofno more than a ramus of a mandible and that part of the' skull withwhich it articulated, a knowledge of this law may enable the paleon-tologist to affirm, with great confidence, that the animal of which itformed a part suckled its young and had non-nucleated red blood-corpuscles ; and to predict that should the back part of that skull bediscovered, it will exhibit two occipital condyles and a well-ossified,basi-occipital bone. •

HUXLEY, ON CLASSIFICATION. 6 7

Deductions of this kind, such as that made by Cuvier in the famouscase of the fossil opossum of Montmartre, have often been verified,and are well calculated to impress the vulgar imagination; so thatthey have taken rank as the triumphs of the anatomist. But itshould carefully be bome in mind, that, like all merely empirical laws,which rest upon a comparatively narrow observational basis, forreasoning from them may at any time break down. If Cuvier, theexample, had had to do with a fossil Thylacinus instead of a fossilOpossum, he would not have found the marsupial bones, though theinflected angle of the jaw would have been obvious enough. And so,though, practically, any one who met with a characteristicallymammalian jaw would be justified in expecting to find the character-istically mammalian occiput associated with it; yet, he would be abold man indeed, who should strictly assert the belief which is im-plied in this expectation, viz. that at no period of the world's historydid animals exist which combined a mammalian occiput with areptilian jaw, or vice versa.

Not that it is to be supposed that the correlations of structure ex-pressed by these empirical laws are in any sense accidental, or otherthan links in the general chain of causes and effects. Doubtlessthere is some very good reason why the characteristic occiput of aMammal should be found in association with mammae and non-nucleated blood-corpuscles; but it is one thing to admit the causalconnection of these phenomena with one another, or with some third;and another thing to affirm that we have any knowledge of thatcausal connection, or that physiological science, in its present state,furnishes us with any means of reasoning from the one to theother.

Cuvier, the more servile of whose imitators are fond of citing hismistaken doctrines as to the nature of the methods of palaeontologyagainst the conclusions of logic and of common sense, has put this sostrongly that I cannot refrain from quoting his words.*

" But I doubt if any one would have divined, if untaught by ob-sei-vation, that all ruminants have the foot cleft, and that they alonehave it. I doubt if any one would have divined that there are frontalhorns only in this class : that those among them which have sharcanines for the most part lack horns.

" However, since these relations are constant, they must have somesufficient cause: but since we are ignorant of it, we must make goodthe defect of the theory by means of observation : it enables us toestablish empirical laws, which become almost as certain as rational

• ' Ossemens fossiles,' ed. 4m", tome l r , p. 164.

6 8 HUXLEY, ON CLASSIFICATION.

laws when they rest on sufficiently repeated observations; so thatnow, whoso sees merely the print of a cleft foot may conclude thatthe animal which left this impression ruminated, and this conclusionis as certain as any other in physics or morals. This footprint alone,then, yields to him who observes it, the form of the teeth, the form ofthe jaws, the form of the vertebras, the form of all the bones of thelegs, of the thighs, of the shoulders, and of the pelvis of the animalwhich has passed by: it is a surer mark than all those of JZadig."

Morphological classification, then, acquires its highest importanceas a statement of the empirical laws of the con-elation of structures;and its value is in proportion to the precision and the comprehensive-ness with which those laws, the definitions of the groups adopted inthe classification, are stated. So that, in attempting to arrive atclear notions concerning classification, the first point is to ascertainwhether any, and if so, what groups of animals can be established,the members of which shall be at once united together and separatedfrom those of all other groups, by well-defined structural characters.And it will be most convenient to commence the inquiry with groupsof that order which are commonly called CLASSES, and which areenumerated in an order and arrangement, the purpose of which willappear more fully by and by, in the following table.

HUXLEY, ON CLASSIFICATION. 69

TABLE OP THE CLASSES OF THE ANIMALKINGDOM.

The Limits of the Fowr Gvmerim Sub-Kingdoms me indicated by the

Brackets and Dotted Line.

EADIATA.

I Gregarimda. Infusoria.

i Mhizopoda (P).

I Spongida.

\ Hydrozoa.

j Aetinozoa.

\ Polyzoa.

Scolecida (?).JEchinodermata.

Annelida.

Crustacea.

Araclinida.

Myriapoda.

Insecta.

AETICULATA.

Brachiopoda.

Ascidioida.

Lamelli branchiata.

Branchiogaateropoda.

Ftdmogasteropoda.

Pteropoda.

Cephalopoda.

MOLLTJSOA. Reptilia.Aves.Mammialia. .

VEETEBEATA.

70 HUXLEY, ON CLASSIFICATION.

I t is not necessary for my purpose that the groups -which, ardnamed on the preceding table should be absolutely and preciselyequivalent one to another; it is sufficient that the sum of them is thewhole of the Animal Kingdom, and that each of them embraces oneof the principal.types, or plans of modification, of animal form; sothat, if we have a precise knowledge of that which constitutes thetypical structure of each of these groups, we- shall have, so far, anexhaustive knowledge of the Animal Kingdom.

I shall endeavour, then, to define—or, where definition is not yetpossible, to describe .a typical example of—these various groups.Subsequently, I shall take up some of those further classificatoryquestions which are open to discussion; inquiring how far we cangroup these elaeaeainto larger.assemblages, with definite and constantcharacters; and, on the other hand, how far the existing subdivisionsof the classes are well based or otherwise. But the essential matter,in the first place, ia to be quite clear about the different classes, andto have a distinct knowledge of all the sharply-definable modifica-tions of animal structure which are discernible in the animal king-dom. . . .

The first class of which I shall speak is the group of the GREGA-RINIDA. These are among the simplest animal forms of which wehave any knowledge. • They are the inhabitants of the bodies for themost part of invertebrate, but also of vertebrate, animals; and theyare commonly to be found in abundance in the alimentary canal ofthe common cockroach, and in earth-worms, They are all micro-scopic, and any one of them, leaving minor modifications aside, maybe said to consist of a sac, composed of a more or less atractureless,not very well-defined membrane, containing a soft semi-fluid sub-Stonce, in the midst, or at one end, of which lies a delicate vesicle;in the centre of the latter is a more solid particle. (Fig. 1, A.) . Nodoubt many persons will be struck with the close resemblance of thestructure of this body to that which is possessed by an ovum. Youmight take the more solid particle to be the representative of thegerminal spot, and the vesicle to be that of the germinal vesicle;while the semi-fluid sarcodic contents might be regarded as the yelk,and the outer membrane as the vitelline membrane. I do not wishto strain the analogy too far, but it is, at any rate, interesting to ob-serve this close morphological resemblance between one of the lowestof animals and that form in which all the higher animals commencetheir existence. I t is a very remarkable characteristic of this group,that there is no separation of the body into distinct layers, or intocellular elements. The Gregarinida are devoid of mouths and ofdigestive apparatus, living entirely by imbibition of the juices of theanimal in whose intestine, or body cavity, they are contained. The

HUXLEY, ON CLASSIFICATION. 71

most conspicuous of those phenomena, which we ordinarily regard assigns of life, which they exhibit, is a certain contraction and expan-sion along different diameters, the body slowly narrowing, and thenlengthening, in various directions. Under certain circumstances(though the conditions of the change are not thoroughly understood),it is observed that one of these Gregarinida, whatever its form maybe, will convert itself into a well-rounded sac, the outer membraneceasing to exhibit any longer those movements of which I spoke,

Fig. 1. A, Gregarina of the earthworm (after Lieberkuhn); B, encysted;C, D, with the contents divided into pseudo-navicellas; E, F, free pseudo-navicelUo; G, H, free amoebiform contents of the latter.

and becoming coated by a structureless investment, or " cyst"(Kg. 1, B).

The substance of the body contained within the cyst next under-goes a singular change. The central nucleus and the vesicle disap-pear ; after a time, the mass breaks up into a series of roundedportions and, then, each of these rounded portions elongates, and,

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72 HUXLEY, ON CLASSIFICATION.

becoming slightly pointed at each end, constitutes a little body•which has been called a " Pseudo-navicella," from its resemblance tothe Diatomaceous Navxnda or Navicella (Fig. 1, C, D). Next, thecapsule bursts and the Pseudo-navicellce (Fig. 1, B, F) are scatteredand passed out of the body of the animal which they inhabit.Though, of course, a great number of them are destroyed, some, atany rate, are devoured by other animals ; and, when that is the case,the little particle of protein substance which is inclosed within thePseudo-navicella is set free from its shell, and exhibits much morelively movements than before, thrusting out processes in variousdirections, and drawing them in again, and, in fact, closely resem-bling one of those animalcules which have been called Amcebce (Fig.1, H). The young Anioebiforrn Gregarina grows, increases in size,and at length assumes the structure which it had at first. That, insubstance, is all that we know of this lowest division of animal life.But it will be observed, there is a hiatus in oui- knowledge. Wecannot say that we know the whole nature and mode of existence ofthis, or any other animal, until we have traced it to its sexual state;tut , at present, we know nothing whatever of this condition amongthe Gregarince; so that in reasoning about them we must alwaysexercise a certain reticence, not knowing how far we may have tomodify our opinions by the discovery of the sexual state hereafter.

The process of becoming encysted, preceded or accompanied veryoften by the mutual apposition of two Gregarinee, was formerlyimagined to correspond with what is termed among plants " conjuga-tion,"—a process which in some cases, at any rate, appears to be ofa sexual nature. But the discovery that a single Chregarina may be-come encysted and break up into Pseudo-navicellcB seems to negativethis analogy.

But now, leaving this, I pass on to the next class—that which isindicated in the table as the RHIZOPODA. I have put a query againstit, as I shall have to return to it as another of those respecting whichour knowledge is incomplete. And at this moment I merely directattention to the salient and characteristic features of the wholegroup (Fig. 2).

I t seems difficult to imagine a stage of organization lower than thatof Gregarinida, and yet many of the Rhizopoda are still simpler. Noris there any group of the animal kingdom which more admirablyillustrates a very well-founded doctrine, and one which was oftenadvocated \>y Hunter himself, that life is the cause and not the con-sequence of organization; for, in these lowest forms of animal life,there is absolutely nothing worthy of the name of organization to bediscovered by the microscopist, though assisted by the beautiful in-struments that are now constructed. In the substance of many of

HUXLEY, ON CLASSIFICATION. 7 3

these creatures, nothing is to be discerned but a mass of jelly, whichmight be represented by a little particle of thin glue. Not that itcorresponds with the latter in composition, but it has that textureand sort of aspect; it is structureless and organless, and withoutdefinitely formed parts. Nevertheless, it possesses all the essentialproperties and characters of vitality ; it is produced from a body likeitself; it is capable of assimilating nourishment, and of exertingmovements. Nay, more, it can produce a shell; a structure, inmany cases, of extraordinai-y complexity and most singular beauty(Fig. 2, D).

That this particle of jelly is capable of combining physical forcesin such a manner as to give rise to those exquisite and almost mathe-matically-arranged structures—being itself structureless and withoutpermanent distinction or separation of parts—is, to my mind, a factof the profoundest significance.

Though a Rhizopod is not permanently organized, however, it canhardly be said to be devoid of organs ; for the name of the group isderived from the power which these animals possess of throwing outprocesses of their substance, which are called " pseudopodia," andare sometimes very slender and of great length (Pig. 2, E), sometimesbroad and lobe-like (Kg. 2, A). These processes may flow into oneanother, so as to form a network, and they may, commonly, be thrustout from any part of the body and retracted into it again.

If you watch one of these animals alive, you see it thrusting out,first one and then another of its pseudopodia, exhibiting changes ofform comparable to those which the colourless corpuscles of thehuman blood present. The movements of these Rhizopods are quiteof the same character, only they are much more extensive and effectlocomotion. The creature also feeds itself by means of its pseudo-podia, which attach themselves to nutritive particles, and then drawthem into the substance of the body. There is neither ingestive noregestive aperture, neither special motor nor prehensile organs, butthe pseudopodia perform each function as it may be required.

But here, again, we labour under an imperfection of knowledge.For, although it is quite certain that the Rhizopoda may multiply bydivision of their substance—in a way somewhat analogous to thatwhich I detailed when speaking of the Gregarinida—yet, as in thatcase, we have no knowledge of any true sexual process. I t is a mostremarkable circumstance that though these animals are abundant,and are constantly under observation, we are still in doubt upon thatessential point,—still uncertain whether there may not be some phasein the cycle of vital phenomena of the Rhizopoda with which we areunacquainted; and, under these circumstances, a perfect definition ofthe class cannot even be attempted.

74 HUXLEY, ON CLASSIFICATION.

The next division is the group of the SPONGIDA, which exist undersuch multitudinous forms in both salt and fresh waters. Up to thelast few years we were in the same case, with respect to this class, aswith the Gregarinida and the Bhizojaoda. Some zoologists even havebeen anxious to relegate the sponge3 to the vegetable kingdom; but

FIG. 2.

Fig. 2. A, B, free and encysted conditions of an Amaba (after Auerbach);E, a Foraminifer (Itotalia) with extended pseudopodia; D, its shell insection (after Schulze).

the botanists, who understood their business, refused to have any-thing to do with the intruders. And the botanists were quite light;for the discoveries of late years have not left the slightest doubt thatthe sponges are animal organisms, and animal organisms, too, of avery considerable amount of complexity, if we may regard as com-

HUXLEY, ON CLASSIFICATION. 75

plex a structure which results from the building up and massingtogether of a number of similar parts.

The great majority of the sponges form a skeleton, which is com-posed of fibres of a horny texture, strengthened by needles, orspicula, of silicious, or of calcareous, matter; and this framework isso connected together as to forcn a kind of fibrous skeleton. Thi3,however, is not the essential part of the animal, which is to be soughtin that gelatinous substance, which invests the fibres of the skeletonduring life, and is traversed by canals which open upon the surfaceof the sponge, directly or indirectly, by many minute, and fewerlarge, apertures.

If I may reduce a sponge to its simplest expression—taking thecommon Spongilla, for example, of our fresh waters,—the structure—removing all complexities, and not troubling ourselves with theskeleton, because that has nothing to do with what we are nowconsidering—may be represented by the diagram (A, Kg. 3). Thereis a thin superficial layer (a) formed entirely of a number of theso-called sponge particles, or ultimate components of the livingsubstance of the sponge, each of which is similar to an Aniceba, andcontains a nucleus. These are all conjoined in a single layer, so asto form a continuous lamellar membrane, which constitutes the outerand superficial layer of the body. Beneath this is a wide cavity,communicating with the exterior by means of minute holes in thesuperficial layer (6), and, of course, filled with water. The cavityseparates the superficial layer of the sponge from its deeper substance,which is of the same character as the superficial layer, being madeup of a number of aggregated sponge particles, each of which has anucleus and is competent to throw out numerous pseudopodial pro-longations if detached. While the living sponge is contained in water,a great number of currents of water set in to the wide cavity beneatha, a, through the minute apertures (b), which have thence beentermed " inhalent."

In the floor of the cavity, there are a number of apertures whichlead into the canals ramifying in the deep layer, and eventuallyending in the floors of certain comparatively lofty funnels or craters.The top of each of these presents one of those larger and less numerousapertures, which have been referred to as existing on the surface of thesponge, and which are fitly termed " exhalent" apertures. For, aaDr. Grant discovered, many years ago, strong, though minute,currents of water are constantly flowing out of these large apertures;being fed by the currents which as constantly set in, by the smallapertures and through the superficial cavity, into the canals of thedeeper substance. The cause of this very singular system of currents,remained for a long tune unknown. I t was rendered intelligible by

HTJXLEY, ON CLASSIFICATION.

Fig. 3. A, Hypothetical section of a SpongUla; a, superficial layer; b, inhalentapertures; e, ciliated chambers; d, an exhalent aperture; e, deeper sub-stance of the sponge. The arrows indicate the direction of the currents.B, a small spongo with a single exhalent aperture, seen from above (afterLieberkuhn); a, inhalent apertures j c, ciliated chambers; d, exhalentaperture. C, a ciliated chamber; D, a free-swimming ciliated embryo.

HUXLEY, ON CLASSIFICATION. 77

Dr. Bowerbank's discovery of the existence of vibratile cilia in thegenus Grcmtia, but it is only quite recently that the precise nature ofthe arrangement of the apparatus which gives rise to these currentsin ordinary sponges, has been made out by Lieberkiihn and byCarter. The canals which enter the deep substance of the spongebecome dilated into spheroidal chambers, lined with sponge particles(Fig. 3, A, o, C), each of which is provided with, a vibratile cilium jand as all these cilia work in one direction—towards the crater—theysweep the water out in that direction, and its place is taken by freshwater, which flows in through the small apertures, and through thesuperficial chamber. The currents of water carry along such mattersas are suspended in them, and these are appropriated by the spongeparticles lining the passages, in just the same way as any one of theRhiziopoda appropriates the particles of food it] finds in the waterabout itself. So that we must not compare this system of aperturesand canals to so many mouths and intestines; but the sponge repre-sents a kind of subaqueous city, where the people are arranged aboutthe streets and roads* in sueh a manner, that each can easilyappropriate his food from the water as it passes along.

In the sponges two reproductive processes are known to occur: theone of them asexual, corresponding with the encysting process of theGregarmida; and the other, truly sexual, and answering to thecongress of the male and female elements in the higher animals. Inthe common fresh-water Spongilla, towards the autumn, the deeperlayer of the sponge becomes full of exceedingly small bodies, some-times oalled " seeds " or " gemmules," which are spheroidal, and have,at one point, an opening. Every one of these bags—in the walls ofwhich are arranged a great number of very singular spicula, eachresembling two toothed wheels joined by an axle—is, in point of fact,a mass of sponge particles which has set itself apart—gone intowinter quarters, so to speak—and becoming quite quiescent, encystsitself and remains still. The whole Spongilla lies down, and theseeds, inclosed in their case, remain uninjured through the winter.When the spring arrives, the encysted masses within the "seed,"stimulated by the altered temperature of the water, creep out of theirnests, and straightway grow up into Spongilla like that from whichthey proceeded.

But there is, in addition, a true sexual process, which goes onduring the summer months. Individual sponge particles becomequiescent, and take on the character of ova; while, in other parts,particular sponge pai-ticles fill with granules, the latter eventuallybecoming converted into spermatozoa.

These sacs burst and some of the spermatozoa, coming into contactwith the ova, impregnate them. The ova develop and grow into

7 8 HUXLEY, ON CLASSIFICATION.

ciliated germa (D, fig. 3), which make their way out, and, afterswimming about for a while, settle themselves down and grow up into

•Ifow that we -know'-the whole cycle of the life of the sponges, andthe characters which may be demonstrated to be common to thewholeof this' important and remarkable class, I do not think any"ofee who is acquainted with the organization or the functions ofplants, will be inclined to admit that the Spongida have the slightest-real affinity with any division of the vegetable kingdom.r The next-group1 to be considered is the division of the INFUSORIA ;rftfid here, again, within the last few years, prodigious strides have:been made in our knowledge of the Bubjeot. Although the Infusoriateuve been favorite ' studies for many years, still it is only quite••reoeritfly 'that the cycle of-life of these animals has been made almostxsowpletely lmown, and that we have beoome acquainted with thetrue sexual .process as it" occurs in them

The different speeies of the -genus Ptwawtceciwn are very commonamong'th'e microscopic- inhabitants of our fresh waters, swimmingabout by mean's of the vibratile ©ilia with which the whole surface oftheir bodies is covered; and the structure which eSseatiaJly charac-terises these animals is probably that which is coniBion to the wholeof the Xnfuaoria.yo that an account of the leaddsg- str'uctaral featuresof Faramoeeiwm-ia, in effect, a definition of those of the fsoup.

Imagine adeMcate, slipper-shaped body inclosed -within asfcructvire-less membrane, or diUeula, which is formed as an excretion upon itsouter surface. At one point (Fig. 4, B a) the body exhibits a slightdepression; leading into a sort of little funnel (b c) coated by a con-tinuation of the same cuticulai- investment, -which stops short at thebottom- of the funnel. The whole of the bag formed by- the cuticulais Kned by a soft layer of gelatinous matter, or " sarcode," which iscalled the "cortical" layer (Fig. 4, A o); while inside that, andpassing into-it qiaifce gradually, there being no sharp line of demarca-tion betweeritbe two,- is a semi-fluid substance, which occupies thewhole of "Hie central region of the body. Neither in the cuticle, thecortical- layer, nor the central substance, has any anatomist yet dis-covered a differentiation into cellular layers, nor any trace of thathistological composition which we meet with in the tissues of thehigher animals; so that-here is' another case of complex vital phe-nomena proceeding from a substance which, in a histological sense,is structureless. ' '•' " •• - • •

At two' points of the body (Fig. 4, A c c) the substance of thecortical layer exhibits a remarkable power of contraction and dilata-tion. If you watch one of those' points, the sarcode suddenly seemsto open like a-wiiidow and,-for a while, a clear space is visible, which

HUXLEY, ON CLASSIFICATION. 79

then; quite suddenly, "shuts again. After a little time $».«. samediastole and systole are repeated. As the systole takes plas«, it }%possible, occasionally, to discern certain radiating canals, whichextend from the cavities into the surrounding sarcode, and disappearagain before diastole occurs. There is no doubt that the clear spaceis a chamber filled with fluid in the cortical layer, and since goodobservers maintain that there is an aperture of communication,through the cuticula, between the ' contractile chamber' and the ex-

Fig. 4. Paramacium bursaria (after Stein). A, the animal viewed from thedorsal side; a, cortical layer of the body; b, "nucleus;" e, contractilechamber; d, d', matters taken in as food; e, chlorophyll granules.

B, the animal viewed from the ventral Bide; a, depression leading to b,mouth; e, gullet; d, "nucleus;" d> "nucleolus;" e, central sarcode. Inboth these figures the arrows indicate the' direction of the circulation of thesarcode.

Ci Paramaciian dividing transversely; a, a', contractile spaces; b, V,*'nucleus" dividing; c, a, "nucleoli."

;erior, this fluid can be little more than water. Perhaps the wholeshould be regarded as a respiratory or secretory mechanism : in oneshape or another, it is eminently characteristic of the Infusoria.Besides this singular apparatus, there lies embedded in another partof the cortical layer a solid mass, of an elongated oral shape (Fig. 4,A B d), which, has been called the " nucleus," though it must becarefully distinguished from the " nucleus " of a cell. Upon one side

80 HUXLEY, ON CLASSIFICATION.

of this, and, as it were, stuck on to it, is a little rounded body (Fig. 4,B d'), which has received the name of the " nucleolus." The animalswims about, driven by the vibration of its cilia, and whatever nutri-ment may be floating in the water is appropriated by means of thecurrent which is caused to set continually into the short gullet bythe cilia which line that tube.

But it is a singular circumstance that these animals have an ali-mentary canal consisting of a mere gullet, open at the bottom, andleading into no stomach or intestine, but opening directly into thesoft central mass of sarcode. The nutritious matters passing downthe gullet, and then into the central more fluid substance, becomesurrounded by spheroids of clear liquid (Fig. 4, A d), consisting ap-parently of the water swallowed with them, so that a well-fed Para-inmciwm exhibits a number of cavities, each containing a little massof nutritious particles. Hence formerly arose the notion that theseanimals possess a number of stomachs. It was not unnaturallyimagined that each of the cavities in question was a distinct stomach ;but it has since been discovered that the outer layer of the sarcodeis by means of some unknown mechanism, kept in a state of constantrotation; so that the supposed stomachs may be seen to undergo aregular circulation up one side of the body and down the othei". Andthis circumstance, if there were no other arguments on the sameside, is sufficient to negative the supposition that the food-containingspaces are stomachs; for it is impossible to imagine any kind ofanatomical arrangement which shall permit true dilatations of analimentary canal to rotate in any such manner. Faecal matters areextruded from an anus, which is situated not far from the mouth, butis invisible when not in use. It is an interesting and importantcharacter of the Infusoria, in general, that, under some circum-stances, they become quiescent and throw out a structureless cystaround their bodies. The Infusorium then not unfrequently dividesand subdivides, and, the cyst bursting, gives rise to a number ofseparate Infusoria.

The remarkable powers of multiplication by fission and gemma-tion which many of the group exhibit are well known; but within thelast few years the investigations of Muller, Balbiani, Stein, andothers, have shown that these minute creatures possess a true processof sexual multiplication, and that the sexual organs are those whichhave been denominated " nucleus " and " nucleolus." The nucleus isthe true ovary—the nucleolus, the testis, in Paramcecium. At par-ticular times, the latter increases very much in size, and its substanceis broken up into rod-like bodies, which represent spermatozoa. TwoInfusoria, in this condition, become conjoined, and the nucleolus(now converted into a spermatic capsule) of each passes into the

HUXLEY, ON CLASSIFICATION. 81

body of the other. The spermatic filaments are said to enter thenucleus, which then enlarges, and either divides into, ov gives off, anumber of rounded germs, which become oval ciliated bodies pro-vided with long processes. These make their way out of the body,and, it is believed, are metamorphosed directly into young Para-vicecia. But, perhaps, further information is required before w e canbe quite certain on this point.

The subsequent lectures in this volume are devoted tothe Molluscous, Annulose, and Vertebrate series of animals.They are treated in the same lucid and original manner asthe lower groups of animals to which the above lecturerelates. We can recommend these lectures to the study ofall young students of natural history who are desirous oftaking a comprehensive view of the structure and relations ofthe animal kingdom. In the second and third lectures,will be found numerous observations on the forms of themolluscous and annulose animals, which will clearly show thatit is only by the aid of the microscope that a proper study ofthe animal kingdom can be undertaken. These lectures byProfessor Huxley are copiously illustrated, and as a workby one of the most advanced students of the science of biology,it cannot fail to be interesting not only to those engaged inanatomical and physiological studies, but to all who take aninterest in the observation of the structure and functionsof the animal kingdom.

JOURNAL OF MICROSCOPICAL SCIENCE.

DESCRIPTION OF PLATE I A,

Illustrating the Rev. W. Houghton's note on Canals in theHead of the Eel.

1,—Head of A, muUroitrii, sbovriug tbe orifices of the canals.a. Anterior orifice, .b. Posterior ditto,

2.—The same, with the soft parts removed, and with a bristle insertedinto each canal.

3.—Side view of same.

d-.—Vertical sectioii of cranium of A. acutirostris.

5.—Membranous fold or liollow iu which the canal terminates.

JOURNAL OF MICROSCOPICAL SCIENCE.

DESCRIPTION OF PLATE I B,

Illustrating Henry Giglioli's paper on some ParasiticalInsects from China.

Fig.

1.—Lipeurus Diomedea, female, about two and a half times larger than

nature; the dorsum is shown.

2.—L. JJiomedeeBi male; the ventral side is exposed.

3.—Docophoroides brevis, female, magnified about three times; ventral

aspect.

4.—D. brevis, male, magnified about three and a half times; dorsal aspect.

5.—Copulating organ of D. brevis, greatly magnified.

C.—Tibia and tarsus of a leg of D. brevis, magnified.

7.—Nirmus mandarinus, magnified seven times; ventral aspect.

8'— „ „ dorsal aspect.

0.—Docophorus mandarinus, magnified about seven limes; dorsal aspect.

10.-—Ornithomyia Chinensis, magnified about two and a half times; ventral

aspect.

11.—Tarsus and claw of 0. Chinensis, magnified.

12.—Strebla molossa, magnified about six times ; ventral aspect.

13.—Polyalenes molossiis, magnified about six times ; dorsal aspect.

14.—Head of JP. molossus, magnified.

15.—Spines from head of P. molossus, magniGed.

TRANSACTIONS OF MICROSCOPICAL SOCIETY.

DESCRIPTION OF PLATES I & II,

Illustrating Dr. Greville's paper on New Diatoms.Series XL

F i g . •

1.—Aulacodiscus

2.—3.— „*•— »5. i,

6.—

Qrevillettnus.

wmbonatus.

ammnus.

radialus.

pellucidw.

orientalis.

7,—Triceratium concinnum.

8.— „ partilum.

9.—BiddulpHa gigantea.

10.—Cocconeis Barbadensis.

11.—Coscinodiscus angulatus.

12.—Terebraria Barbadensis, front view.

13.— „ „ side view.

All the figures are x 400 diameters.

TRANSACTIONS OP MICROSCOPICAL SOCIETY.

DESCRIPTION OF PLATE III,

Illustrating Mr. Lauder's paper on New Diatoms.

Kg.1.—Perfect filament of Bacteriasktwi varians.

2 a.—Terminal cells.2 *.—Separate awn.3 a.—Intermediate cell.3 b.—Separate awn.

4.—Terminal cells.5.—Frustules of B. varians.6.—Sporangium of same.

7 a.—S. hyalinum.7 b.—The same.

8.—Species of Chactoceros.

TRANS. MICR. SOC, VOL. XII., N.S., PL. VI.

Fig, 3.

Vibratlle Filaments and minute particles con-sisting of Viscid Coliured Mutter. Mood

Corpuscles of Human Subject, x 1800.

Fig. 4.

Curious changes in form of EedBlood Corpusclesof the Frofr, resulting from exposure to heat.Tlie thin filaments of the red viscid matterwere

inconstautaudverysctivevihration. x 700.

Fig. 5. Fig. 6.

Disintegration of the Rod Blood Corpuscles of tlioGuinea Fig, rcsultini; from hesit. Sonic have sena-ratcd into several small particles, each of which has

assumed the crystalline form, x 700.

Fig. 8.

Ks Jilo'od j.ro'b'aHyVei-y jrouiKt'n'ea Corpuscles')!surrounded by ordinary Red JJlood Corpuscles.

1000th of an inch ~i1000th of ;m inch 1 •