[897] Isidore Geoffroy St. Hilaire, 'Hist. des Anomalies,' tom. ii. pp. 549, 560, 562; Virchow, idem, p. 484.
[898] For the most recent classification of cells, see Ernst Häckel's 'Generelle Morpholog.,' Band ii., 1866, s. 275.
[899] 'The Structure and Growth of Tissues,' 1865, p. 21, &c.
[900] Dr. W. Turner, 'The present Aspect of Cellular Pathology,' 'Edinburgh Medical Journal,' April, 1863.
[901] This term is used by Dr. E. Montgomery ('On the Formation of so-called Cells in Animal Bodies,' 1867, p. 42), who denies that cells are derived from other cells by a process of growth, but believes that they originate through certain chemical changes.
[902] Prof. Huxley has called my attention to the views of Buffon and Bonnet. The former ('Hist. Nat. Gén.,' edit. of 1749, tom. ii. pp. 54, 62, 329, 333, 420, 425) supposes that organic molecules exist in the food consumed by every living creature; and that these molecules are analogous in nature with the various organs by which they are absorbed. When the organs thus become fully developed, the molecules being no longer required collect and form buds or the sexual elements. If Buffon had assumed that his organic molecules had been formed by each separate unit throughout the body, his view and mine would have been closely similar.
Bonnet ('Œuvres d'Hist. Nat.,' tom. v., part i., 1781, 4to edit., p. 334) speaks of the limbs having germs adapted for the reparation of all possible losses; but whether these germs are supposed to be the same with those within the buds and sexual organs is not clear. His famous but now exploded theory of emboîtement implies that perfect germs are included within germs in endless succession, pre-formed and ready for all succeeding generations. According to my view, the germs or gemmules of each separate part were not originally pre-formed, but are continually produced at all ages during each generation, with some handed down from preceding generations.
Prof. Owen remarks ('Parthenogenesis,' 1849, pp. 5-8), "Not all the progeny of the primary impregnated germ-cell are required for the formation of the body in all animals: certain of the derivative germ-cells may remain unchanged and become included in that body which has been composed of their metamorphosed and diversely combined or confluent brethren: so included, any derivative germ-cell, or the nucleus of such, may commence and repeat the same processes of growth by imbibition, and of propagation by spontaneous fission, as those to which itself owed its origin;" &c. By the agency of these germ-cells Prof. Owen accounts for parthenogenesis, for propagation by self-division during successive generations, and for the repairs of injuries. His view agrees with mine in the assumed transmission and multiplication of his germ-cells, but differs fundamentally from mine in the belief that the primary germ-cell was formed within the ovarium of the female and was fertilised by the male. My gemmules are supposed to be formed, quite independently of sexual concourse, by each separate cell or unit throughout the body, and to be merely aggregated within the reproductive organs.
Lastly, Mr. Herbert Spencer ('Principles of Biology,' vol. i., 1863-4, chaps. iv. and viii.) has discussed at considerable length what he designates as physiological units. These agree with my gemmules in being supposed to multiply and to be transmitted from parent to child; the sexual elements are supposed to serve merely as their vehicles; they are the efficient agents in all the forms of reproduction and in the repairs of injuries; they account for inheritance, but they are not brought to bear on reversion or atavism, and this is unintelligible to me; they are supposed to possess polarity, or, as I call it, affinity; and apparently they are believed to be derived from each separate part of the whole body. But gemmules differ from Mr. Spencer's physiological units, inasmuch as a certain number, or mass of them, are, as we shall see, requisite for the development of each cell or part. Nevertheless I should have concluded that Mr. Spencer's views were fundamentally the same with mine, had it not been for several passages which, as far as I understand them, indicate something quite different. I will quote some of these passages from pp. 254-256. "In the fertilised germ we have two groups of physiological units, slightly different in their structures."... "It is not obvious that change in the form of the part, caused by changed action, involves such change in the physiological units throughout the organism, that these, when groups of them are thrown off in the shape of reproductive centres, will unfold into organisms that have this part similarly changed in form. Indeed, when treating of Adaptation, we saw that an organ modified by increase or decrease of function can but slowly so react on the system at large as to bring about those correlative changes required to produce a new equilibrium; and yet only when such new equilibrium has been established, can we expect it to be fully expressed in the modified physiological units of which the organism is built—only then can we count on a complete transfer of the modification to descendants."... "That the change in the offspring must, other things equal, be in the same direction as the change in the parent, we may dimly see is implied by the fact, that the change propagated throughout the parental system is a change towards a new state of equilibrium—a change tending to bring the actions of all organs, reproductive included, into harmony with these new actions."
[903] M. Philipeaux ('Comptes Rendus,' Oct. 1, 1866, p. 576, and June, 1867) has lately shown that when the entire fore-limb, including the scapula, is extirpated, the power of regrowth is lost. From this he concludes that it is necessary for regrowth that a small portion of the limb should be left. But as in the lower animals the whole body may be bisected and both halves be reproduced, this belief does not seem probable. May not the early closing of a deep wound, as in the case of the extirpation of the scapula, prevent the formation or protrusion of the nascent limb?