Obrazy na stronie

mark of species. Thus, to select a striking example, Mr. Gosse makes two distinct species of the orangedisked and orange-tentacled anemones, naming them Venusta and Aurora; but as if to prove the indifference of all such characteristics, I brought with me from Tenby an orange-disked-and only onee—which, before it had been home a fortnight, I discovered, with great surprise, was changed into an orange-tentacleddisc and tentacles being of a rich orange hue, the only traces of white remaining just at the tips. If there had been any other specimen in the vase I might have doubted; but having only one in company with a white daisy, and a smooth anemone, there was no avoiding the conclusion.

seems to hesitate on the point, adding, "but it is asserted by numerous authorities that the young are not unfrequently born alive. I not only assert this, but ask whether any one has ever seen the contrary. It startled me, however, when, on opening an anemone, I for the first time saw a young one drop out, and immediately expand its tentacles; and some days afterwards, as I was carrying home a lovely "gem," I saw first one, then two, three, four, seven young ones issue from its mouth, fix themselves at the bottom of the vase, and make themselves at home; they were of various sizes, and in various stages of development. Since then, I have repeatedly witnessed this mode of birth and one day, seeing something in the inside of the tentacle of a Daisy, I snipped the tentacle off, and found a young daisy there. Some writers imagine that the young issue through the orifices at the tips of the tentacles -a supposition not very credible. The truth is, that at the bottom of the stomach there is a large opening -not several minute openings as we see figured in books-through which the young pass from the general cavity into the water; and this appears to me the only exit for the young. Without absolutely denying that the ova are extruded, and their early development carried on out of the parent's body, I have never been able to detect ova, except within the parent. The most curious of all my observations on this point was the finding in the visceral cavity of a smooth anemone a young one as large as a cherry; and to complete the marvel, it was faintly striped with green, like the well-known" greenstriped variety," although its parent was of a dark-brown hue. Could the old one have swallowed an errant youth by mistake? No. It had been many weeks in captivity, where no such errant youths were within reach besides, anemones do not swallow each other; cannibalism belongs to a higher grade of development. Apropos of this peculiarity of colour, I may remark on the great variations observable in the colour of anemones, and the impropriety of making colour the distinguishing


The reader was promised "New Facts," and those already furnished will show him how great an accession to our knowledge may be anticipated from the present direction of so many minds towards these animals; what is written in the best books must be accepted as only suggestions of a few observers, to be controlled by the investigations of succeeding observers. Many problems await solution; many stereotyped assertions must be disproved. Let us here consider one or two accepted "facts" which will turn out to be "fancies" when rigorously examined.

Perhaps nothing has excited more surprise on the part of the public, and nothing has been more unanimously believed by anatomists, than the hypothesis that certain minute organs found in Polypes, and variously styled thread capsules, filiferous capsules, or urticating cells, are organs of urtication, or stinging. The uncritical laxity with which this hypothesis has been accepted may point a lesson. I do not allude to the acceptance of the fact that certain capsules containing threads are found in Polypes, but to the acceptance of the alleged purpose or function of these capsules. The things are there, sure enough; but whether they serve the urticating purpose is another matter. Ever since they were first described by

Wagner, Erdl,t Quatrefages, and Siebold, they have passed without challenge. They have been detected in the whole group of Polypes, in Jelly-fishes, in the papillæ of Eolids, and, according to Vander Hoeven, in Planaria; yet, as far as my reading extends, not one single experiment has been made to prove the function so unanimously admitted, not a single test has been applied to strengthen or controvert what was, indeed, very plausible, but only plausible, not proven. Accordingly, no sooner did I submit the question to that rigorous verification which science imperiously requires, than it became clear to me that my illustrious predecessors -Wagner, Erdl, Siebold, Quatrefages, Ehrenberg, Agassiz, and Owen -men whom the most presumptuous would be slow to contradict, had admitted the point without proof, because it wore so plausible an air. Let me hope the reader will accuse me of no immodesty in thus controverting men so eminent; he will see that whereas they have only hypothesis on their side, I have the accumulated and overwhelming weight of experimental evidence.



What are these "capsules," or "urticating cells?" The uninstructed reader may be told that the Polypes are supposed to urticate, or sting, like nettles; and the nettling organs, or urticating cells, are supposed to be minute suboval microscopic capsules, quite transparent, containing within them threads coiled up, which, on pressure, dart out to many times the length of the capsule, into which they never return. This thread Agassiz likens to a lasso thrown by the polype to secure its prey. I will not enter here into minute details of structure, which would only confuse the reader, who, if curious, will find all that is known, in the works of Mr Gosse, and the treatises of Owen, Siebold, and Rymer Jones. Any one who has once seen these threads under the microscope darting out with lightning rapidity, especially if he uses a high power, and detects the hooks

with which some of them seem to be furnished, will at once admit that the hypothesis of the "nettling" or "urtication" being performed by these threads is an hypothesis so obvious, an explanation so natural, that-it should be doubted. In all complex matters, we should mistrust the obvious explanation; I do not say that we should disregard or reject it, but mistrust it. When we know, on the one hand, that the jelly-fish stings, and when, on the other hand, we know that it is furnished with numerous cells, in which are coiled threads, to be seen darting out when pressed, the idea of connecting the stinging with these threads is inevitable: but this is not enough for science; it is only a preparatory guess, which proves nothing; it may be right, it may be wrong. I believe it is altogether wrong. We have already seen how erroneous was the supposition that Polypes paralysed their victims with a touch; that poison was secreted by their tentacles; yet for this supposition there was at least the evidence of partial observation, whereas, for the supposition we have now to consider, there is absolutely no evidence at all.

WIEGMANN's Archiv., 1835, ii. p. 215.

On a survey of the place where these "urticating cells" are present, we stumble upon an unlucky fact, and one in itself enough to excite suspicion. They are present in a few jelly-fish-which urticate; in actinia which urticate; and in all polypes which, if they do not urticate, are popularly supposed to do so, and at any rate possess some peculiar power of adhesion. In all these cases organ and function may be said to go together. But the cells are also present in the majority of jelly-fish, which do not urticate; in Eolids-which do not urticate; and in Plana. -which do not urticate. Here, then, we have the organ without any corresponding function; urticating cells, but no urtication. The cautious mind of Owen had already warned us that there was something not quite satisfactory in our supposition; "some super

+MULLER'S Archiv., 1841, p. 423.

Comp. Anat., i. p. 39 (English Trans.)

taneously on the slightest pressure;
in point of fact it frequently cannot
be pressed out at all, even when the
whole force of the finger is exerted
on the two pieces of glass between
which it lies. From the very capri-
cious way in which the threads dart
out while under the microscope, and
not under pressure, and from the fre-
quent impossibility of pressing them
out, I suspect that pressure has really
nothing normally to do with the ejec-
tion of the thread.

addition to the thread-cell would seem to be essential to the urticating faculty," he says, when speaking of the jelly-fish, "since these cells are present in species and parts that do not sting." It is to be regretted that he was not moved by this doubt to a closer examination of the evidence on which the urticating faculty rested; he would assuredly have been led to the belief that no superaddition to the thread-cell will account for the phenomenon.

But I waive the argument derived from such a source, and, confining myself to the anemones, ask the reader what he thinks of this awkward fact, namely, that these urticating cells are most abundant in parts which do not urticate? Only the tentacles have this power, and although they have numerous cells, the urtication cannot well be attributed to them, since these cells are more abundant in the convoluted bands, in the lining walls of the stomach, and in the blue spots which surround the oral disc in the smooth anemone-these spots, indeed, being made up of such cells and small granules-yet in not one of these parts can the slightest urtication be traced! How is this? If these cells are the nettling organs, why do they not nettle in those parts where they are most abundant? No one has thought of asking this question.

Hitherto we have merely considered facts of observation; we shall now see them confirmed by experiment. Mr. Gosse proposes to establish a new genus, named Sagartia, on this purely hypothetical function; including in it all those anemones which, like the Daisy and Dianthus, possess an abundance of peculiar white filaments, visible to the naked eye, which are protruded from the pores of the body and the mouth, when the animal is These filaments roughly handled. are seen, on examination, to be chiefly composed of the "urticating cells." Mr. Gosse names the genus Sagartia, because Herodotus says of the Sagartians, that "when they engage with the enemy they throw out ropes which have nooses at the end, and whatever any one catches he drags towards himself, and they that are entangled in the coils are put to death." The name, you perceive, is aptly chosen, that is, it would be, if the hypothesis of the filaments were not a figment. The filaments have no such lasso-like and murderous power. This Mr. Gosse would deny; and I remember he somewhere records an observation which would perhaps quite satisfy him that his denial has good He relates that ground to stand on. he once saw a small fish in the convulsions of agony, with one of these filaments in his mouth; it shortly expired, and he unhesitatingly concludes from this fact that the Sagartia "will attack even vertebrate animals." It is a matter of surprise and regret that Mr. Gosse, having once made such an observation, did not feel the imperative necessity of repeating and varying the fact, so as to be sure that the death was not a mere coinciIf the filament had the power dence. which this single observation fairly

It thus appears that animals having the cells, have none of the power attributed to the cells; and that even in those animals which have the power, it is only present in the tentacles, where the cells are much less abundant than in parts not manifesting the power: the conclusion, therefore, presses on us that the power does not depend upon these cells. And this conclusion is strengthened every step we take. Thus the Anthea is of all anemones the most powerfully urticating; yet if we compare its cells with those of other anemones, we find them greatly inferior in quantity to those of the Daisy and Dianthus, and much inferior in size to those of Crassicornis, as well as less easily made to recoil their threads. It has not been remarked, that whereas according to theory the thread should dart out almost instan

[ocr errors]


seemed to suggest, nothing could be easier than to establish the fact by experiment. But, I repeat, no one has seen the necessity for the verification of an hypothesis so plausible; and Mr. Gosse, like all his predecessors, was content with recording his observation, as if it carried the point. Not being so content, I tested it thus: After irritating a dianthus till it sent out a great many filaments, dropped a very tiny annelid among them, and entangled it completely in their meshes. Yet lo! these filaments, which are said to possess so powerful a faculty of urtication that even vertebrate animals are killed by them, had no other effect upon a soft annelid than that of detaining it in their meshes, from which it shortly freed itself and wriggled away unhurt. Nor was I yet satisfied; placing a tiny crustacean, of the shrimp family, among the filaments of another dianthus, I saw it remain there enveloped, but apparently quite comfortable, not in the least so desirous of escaping as one would expect if it were being "nettled" all over; and when I lurched the jar it swam away. I have since repeated this experiment with entomostraca and annelids without once detecting the slightest indication of their being more incommoded by the filaments than they would have been by threads of silk. Mr. Gosse, indeed, not only maintains that these filaments are weapons of offence, but he actually goes so far as to suggest that the blue spherules which surround the disc of the Mesembryanthemum may "represent the function of these missile filaments" because they are composed of the thread capsules. But I repeat, the hypothesis which assigns to the thread capsules a function of artication or prehension, is an hypothesis without a single fact to warrant it, and is contradicted by the various facts I have just adduced. Ehrenberg has very unwarrantably given an ideal figure of a hydra in the act of seizing its prey, with the hooks of the thread-cell extended; but, as Siebold truly remarks, the animal is never seen thus; and I will add that it is always seen in precisely the

contrary aspect, namely, the blunt end of the cell being in contact with the animal, the hook and thread being turned towards the polype.

I have reserved one fact as the coupde-grace. Having shown that the parts most abundantly supplied with these "urticating cells" do not urticate, I can now remove the last vestige of doubt by the fact that the cell itself from the tentacle of an anemone, when seen to eject the thread and touch an animalcule, does not kill or disable that animalcule; a fact I witnessed when examining the cells under the microscope. This not only gives the coup-de-grace to the general hypothesis, but even sets aside that suggestion of Professor Owen's respecting the probable superaddition to the urticating cell which is to distinguish it from cells in those parts destitute of the power.

The foregoing discussion has had a purpose beyond that of rectifying an universal error-the purpose of pointing a lesson in comparative anatomy. The greatest living experimental physiologist, Claude Bernard, has recently insisted with emphasis on the importance of recognizing "anatomical deduction" to be a fruitful source of error.* He warns us against attempting to deduce a function from mere inspection of the organ, without seeing that organ in operation, and applying to it the test of experiment. As a case of pure deduction, this hypothesis of the urticating cells" seemed to command, and did command, instantaneous assent; but on submitting it to verification, we find the hypothesis to be an error. To the philosophical mind, therefore, there will have been an interest in the foregoing discussion greater than any interest issuing out of the mere conclusion respecting the thread-capsules.

There are other new facts which were yielded to patient investigation, but, having limits necessarily somewhat circumscribed, this Magazine cannot contain all facts, even were its readers of unappeasable appetite; so I will confine myself to the single discovery of the reproductive system in the anemones, that being of some

*Leçons de Physiologie Experimentale, vol. ii. 1856.

of a series of investigations. That the reader may follow clearly the course of reasoning presently to be traced, it is necessary to begin with a few explanations which the better instructed will pardon. Let us first fix in our minds a definite idea of the structure of the anemone, as far as it will be involved in the subsequent remarks. Imagine a glove expanded into a perfect cylinder by air, the thumb being removed, and the fingers encircling, in two or three rows, the summit of the cylinder, while at the base the glove is closed by a flat surface of leather. If now on that disc which lies within the circle of fingers we press the head of a pencil-case, and so force the elastic leather to fold inwards, and form a sort of sac suspended in the cylinder, we have by this means made a mouth and stomach; we then cut a small hole at the bottom of the sac, and thus make a free communication with the general cavity. We then divide thi general cavity by numerous partitions of card attached to the wall of the cavity, and form a number of separate chambers called the interseptal spaces. Just as the cavity of the finger is continuous with the cavity of the glove, so are the cavities of the tentacles continuous with the interseptal spaces. In these spaces will be found long coils of delicate membrane, which are sometimes seen lolling out of the mouth, and always bulge out when the anemone is cut open; these are called the convoluted bands, and to them attention is particularly directed. If the reader will now look at the diagram in Mr. Tugwell's Manual (Plate II., fig. 4), in Rymer Jones, or indeed in any modern work on zoophytes (wrong as these diagrams are in several details) he will have a tolerably accurate conception of the general structure of an Actinia.

importance in itself, and helping to illustrate the need there is for rigor ous scepticism and extended observation, on the part of zoological students. So long as we unsuspectingly accept what is repeated in books, without being assured that the statements are made on sufficient evidence, and so long as we have eyes but observe not, zoological progress will necessarily be slow, in spite of the vast number of excellent observers and workers who do accelerate our progress by genuine work. When I insist on the necessity for circumspect doubt, and verified observation, the reader must not understand me as implying that this necessity is not vividly present to the mind of many zoologists, and of every real worker; for in truth, only by such methods can any solid result be reached, and no one even superficially acquainted with the present state of zoology will be disposed to underrate the importance and extent of that band of distinguished investigators whose researches daily unfold fresh discoveries. Not, therefore, as throwing any shadow of scorn on these men and their methods; nor as if I were bringing a neglected principle into prominence, am I tempted to insist on the only method of successful pursuit in these studies; but simply to distinguish by it the students of zoology who wish to increase the circle of knowledge by some small addition of new fact, from students who wish merely to ascertain what is known. In zoology, as in all other departments of intellectual, activity, there are men contented with "information," whose ambition never passes beyond erudition. They want to know what is known. Others there are who, less solicitous, it may be, about what is known, are intensely moved to know for themselves; and these are the workers who extend the circle of the known.

What is known of the reproductive system of anemones? Not much, and that little confusedly. The text-books are somewhat precise; but the precision is for the most part that of error. I carried with me to the coast this amount of definite error, which gradually revealed itself as error in the course

Certain general facts must now be borne in mind. First, let me call attention to the fact that in all animals, the highest as the lowest, the envelope is of eminent importance, its predominance bearing a precise ratio to the simplicity of the organism. The simplest organisms breathe, exhale, secrete, absorb, and reproduce by their envelopes alone; and if the

« PoprzedniaDalej »