becomes divided into oval masses and enclosed by the filamentary extremities of the eight oviducts. Individual development is checked and arrested at the apterous larval condition. It is plain, therefore, that the essential condition of the development of another embryo in this larva is the retention of part of the progeny of the primary impregnated germ-cell."-p. 70.

This view of Owen, so ingeniously advanced, and which he has made subservient for the chief support of his new doctrine of Parthenogensis, is indeed plausible and seems at first satisfactory: but, as I hope to show, it will not bear analysis.

In the first place, it is evident that Owen does not recognize any physiological difference between a bud and an ovum; this is clear from what he remarks in the first quotation, but in his work on Parthenogenesis he has said so in as many words. "The growth by cell-multiplication producing a bud, instead of being altogether distinct from the growth by cell-multiplication in an egg, is essentially the same kind of growth or developmental process. p. 45.

Here is a fundamental error which, if not removed, will obscure all our views of the physiology of reproduction. I have already insisted upon the necessity of this broad distinction between these two forms, a necessity based not only upon differences of anatomical constitution, but also upon physiological signification. An Ovum is the exclusive product of an individual of the female sex, and is always formed in a special organ called the ovary. It is the particular potential representative of the female, and has its ulterior development only from its conjunction with a corresponding element of the opposite or male sex; and zoology presents no instance where there is development from eggs, unless these conditions of the two sexes are fully carried out.

A Bud, on the other hand, is simply an offshoot from the form on which it rests, a portion of the animal capable of individual development. It sustains, therefore, no relations to sex, and, in truth, is widely separated in its ulterior signification from that cycle of processes conceived in a true oviparous reproduction.

All physiologists who have carefully studied embryological and developmental processes, must feel the correctness and importance of this distinction which lies in realities and not in words.

It is true that a bud and an ovum are composed each of the same elements,-simple nucleated cells; but in one, these cells are simply in a mass, while in the other, they have, throughout the animal kingdom, high or low, a definite and invariable arrangement. Then again as to the constitution of each and both being, on the whole, of nucleated cells, it may be said, that it could hardly be conceived to be otherwise, for nucleated cells are the elementary components of all functional organized forms; and it may be added, moreover, that he knows little of the high

est physiology who has not learned that widely different teleological significations may be concealed beneath isomorphic animal forms.

I have thus dwelt rather lengthily upon this point because I think it is a vital one in our subject, and the possession of clear ideas thereon will be found singularly conducive to our correct appreciation of this whole class of anomalous phenomena under discussion. But we will revert to the subject of Owen's hypothesis.

As to the chief point in this hypothesis, the continuation of the primary germ-mass as a leaven, from brood to brood, it requires but little thought to perceive that it is physically impossible. I would first allude to Owen's statement, quoted above, that a portion of the germ-mass is taken into the abdomen of the embryo Aphis, and as he thinks, assumes, without any change, the position of the ovarium. By this he refers, undoubtedly, to the vitellus-looking mass I have described in my observations, and according to which, also, it appeared to serve only as the nutritive material out of which the digestive organs and the germs are formed. Moreover, I feel quite sure that the germ-cells are new cells formed in the abdomen, and not those derived from the parent.

But the point I wish to enforce, is, that even admitting that individuals B may contain an actual residue of individuals A, it is clearly evident that this succession must stop with brood B; for these residual germ-cells which compose B in its earliest condition are lost in the developmental processes, and the germs of individuals C, which are found in B, are, each, primarily, nucleated cells formed de novo, as I have observed and above described. With these observed conditions of development, it is impossible for the individuals of the successive broods to inherit the original spermatic force in the continuation of the original cells.

The hypothesis of Owen, therefore, plausible and ingenious as it may seem, does not appear to me to accord either with observed facts, or with the soundest physiology of the reproductive processes. I may here remark also, that his doctrine of Parthenogensis, based as it is upon the conditions of the hypothesis in question, cannot, as such, be sustained, for the same reasons, and all its phenomena would appear to find their solution either in Steenstrup's doctrine of "Alternation of Generations," so-called, or in the conditions of true gemmiparity-admitting, provisionally, that Steenstrup's doctrine, and gemmiparity, include really different physiological conditions.

But the most important explanation advanced, and the last which I shall notice, is that offered by Steenstrup* in his doctrine

*On the Alternation of Generations, or the Propagation and development of Animals through Alternate Generations, a peculiar form of fostering the young in the lower classes of Animals. Transl. by the Ray Society, London. 1845-passim. SECOND SERIES, Vol. XVII, No. 49.-Jan., 1854.

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of the "Alternation of Generations," and of which it forms a chief support. The details of this peculiar doctrine of Steenstrup I need not here furnish; they are well known to all physiological anatomists. Its features, however, may be expressed in a formula-like manner. Individuals A, produce true fecundated eggs, from which are hatched individuals B, which are unlike their parents in all zoological respects, but in which are developed spontaneously and without any reference to sex, germs which ultimately become individuals like A, and so the cycle of development is completed. These intermediate individuals, B, Steenstrup has termed nurses (Amnen), and he regards them as distinct animals subservient for a special end; he therefore considers that B constitutes a real generation.

Instances of such phenomena are found in the lower orders of the animal kingdom-Polyps, Acalephs and Worms; and late research has shown that they are more or less common throughout the whole of the Invertebrata.

The difference between alternation of generation and metamorphosis is too marked to require illustration; in the latter there is the same individual throughout, and the developmental processes, although concealed beneath different exteriors, are regular and normal; with the former, however, this chain of development is broken by one form being developed in another, this intermediate form serving as a stepping-stone for a higher and ulterior development. Another important point in this alternate reproduction, is, that in each new change some real progress is made the nursing-form being manifestly inferior to the individual to which it gives rise.

Steenstrup regards the Aphides as furnishing the most perfect examples known of nursing individuals, and, on the whole, as constituting typical illustrations of this doctrine he has advanced.*

But if this doctrine implies conditions other than those which belong to true gemmiparity, it does not appear to me that it has any support in the phenomena in question of the Aphides. And although I am inclined to believe, as I shall soon show, that all these phenomena, essentially, may be of the same nature, yet there can be no doubt that the manifestations are here somewhat peculiar. With the Aphides there is no real morphological progress made in each brood, for the viviparous individuals are, zoologically, as perfect in every way, as those which are oviparous, except in their want of true sexual generative organs. I have shown that, in the one species here described, they had well developed wings like the true sexual individuals. Moreover, each brood, from the first to the last, inclusive, is merely a repetition of the same. But these conditions are external and economical, and, instead of offering these prominent examples as evidence against the validi

*See, Steenstrup, loc. cit., p, 112.

ty of Steenstrup's doctrine, I would rather present them as broadly indicating that, after all, this doctrine in question involves no conditions excepting those belonging to a modified form of gemmiparity. All the instances of Polyps, Acalephs, Worms, Insects, &c., all would then be classed in the same category, and the variations in manifestation would belong rather to the economical relations of the animal, than to any intrinsic difference of physiological process. Thus the Distoma-nurses instead of being developed to a condition resembling at all their parent, remain persistent on a low form, and not only is their whole zoological character undeveloped, but they also experience morphological changes from the developmental process which immediately go on within them. All this is in perfect keeping with their economy, as animals, for the low order of their conditions of life does not necessitate a higher and more truly zoological form of these nurses from which are to be developed the true animals; were it otherwise, I cannot but believe that both the nurses and the grand-nurse of Distoma, would quite resemble the original animals. In the case of the Aphides, the economical conditions are different, and finely illustrate this point.

The Aphis-nurse, in virtue of its very typical structure as an insect, must live under higher conditions, and so its development, zoologically, proceeds to a corresponding point; this point is where it, as an insect and as an Aphis, can furnish the nutritive material for the development of its endogenous germs.

Herein, then, would appear to consist the prominent morphological differences observed in this category of phenomena, and I need not labor further to show that they are irrelevant of the primary essential conditions of these curious processes.

Such appears to me to be the highest, both physiological and zoological, interpretation that can be advanced for these phenomena which Steenstrup has so ingeniously collected and collated; and to advance the view that these intermediate individuals or nurses, are not intrinsically and zoologically the same as their parents, but furnish examples of how dissimilar animals may arise. from a common stock-to put forth this view, I say, is to advocate a doctrine in physiology, as mischievous as it is deeply erroneous. I think, therefore, that the doctrine of Steenstrup may prove to be unfounded as far as it would involve, intrinsically, new phenomena in the processes of reproduction; and, as I have said on a preceding page, all its conditions may find their illustration and solution in the various phases of gemmiparity.*

* This statement is made perhaps more strongly and exclusively than the present state of our knowledge would warrant, but I throw it out much in a suggestive way. There is no subject in Physiology more interesting and comprehensive than that of Gemmation; the important question now is, does it, as an individual process, embrace all the categories of phenomena treated by Lovin, Steenstrup, &c., these phenomena varying extrinsically, according to economical conditions, or do they (the phenomena) imply something beyond and dissimilar from gemmation?

If in this discussion of some of the highest relations of physiology, we have not wandered too far from our subject proper which we have thereby sought to illustrate indirectly, we will revert to the thread of its discourse for a few concluding remarks.

The final question now is, what is the legitimate interpretation to be put upon the reproductive phenomena of the Aphides we have described? My answer to this has been anticipated in the foregoing remarks. I regard the whole as constituting only a rather anomalous form of gemmiparity. As already shown, the viviparous Aphides are sexless; they are not females, for they have no proper female organs, no ovaries and oviducts. These viviparous individuals, therefore, are simply gemmiparous, and the budding is here internal instead of external as in the Polyps and Acalephs; it, moreover, takes on some of the morphological peculiarities of oviparity, but all these dissimilar conditions are economical and extrinsic, and do not touch the intrinsic nature of the processes concerned therein.

Viewed in this way, the different broods of Aphides cannot be said to constitute as many true generations any more than the different branches of a tree can be said to constitute as many trees; on the other hand, the whole suite from the first to the last constitute but a single true generation. I would insist upon this point as illustrative of the distinction to be drawn between sexual and gemmiparous reproduction. Morphologically, they have, it is true, many points of close resemblance; but there is a grand physiological difference, the true perception of which is deeply connected with our highest appreciation of individual an-imal life.* A true generation must be regarded as resulting only from the conjugation of two opposite sexes-from a sexual process in which the potential representations of two individuals are united for the elimination of one germ. This germ-power may be extended by gemmation or by fission, but it can be formed only by the act of generation, and its play of extension and prolongation by budding, or by division, must always be within a certain cycle, and this cycle is recommenced by the new act of the conjugation again of the sexes.

In this way, the dignity of the ovum as the primordium of all true individuality is maintained; and the axiom of Harvey, omne vivum er ovo, stands as golden in physiology. The buds may put on the dress and the forms of the ovum, but these resemblances are extrinsic and in fact only an inheritance from their great predecessor.

In this view as well as in several others herein discussed, I am pleased to say that I have the support of so learned a physiologist as Dr. Carpenter. See his Review "On the development and Metamorphoses of Zoophytes" in the Brit. and Foreign Med. Chir. Rev., 1848, i. p. 183; and "On Reproduction and Repair" in Ibid. 1849, i, p. 419.