E V L U T I N 745 contains an excessively minute but complete chick ; and that fecundation and incubation simply cause this germ to absorb nutritious matters, which are deposited in the interstices of the elementary structures of which the miniature chick, or germ, is made up. The consequence of this intussusceptive growth is the "development" or " evolution" of the germ into the visible bird. Thus an organized individual (tout organise] " is a composite body consisting of the original, or elementary, parts and of the matters which have been associated with them by the aid of nutrition;" so that, if these matters could be extracted from the individual (tout), it would, so to speak, become concentrated in a point, and would thus be restored to its primitive condition of a <jerm; "just as, by extracting from a bone the calcareous substance which is the source of its hardness, it is reduced to its primitive state of gristle or membrane." 1 " Evolution " and " development " are, for Bonnet, synonymous terms; and since by " evolution" he means simply the expansion of that which was invisible into visibility, he was naturally led to the conclusion, at which Leibnitz had arrived by a different line of reasoning, that no such thing as generation, in the proper sense of the word, exists in nature. The growth of an organic being is simply a process of enlargement, as a particle of dry gelatine may be swelled up by the intussusception of water; its death is a shrinkage, such as the swelled jelly might undergo on desiccation. Nothing really new is produced in the living world, but the germs which develop have existed since the beginning of things; and nothing really dies, but, when what we call death takes place, the living thing shrinks back into its germ state. 2 The two parts of Bonnet s hypothesis, namely, the doctrine that all living things proceed from pre-existing germs, and that these contain, one inclosed within the other, the germs of all future living things, which is the hypothesis of "emboitement;" and the doctrine that every germ contains in miniature all the organs of the adult, which is the hypothesis of evolution or development, in the primary senses of these words, must be carefully distinguished. In fact, while holding firmly by the former, Bonnet more or less modified the latter in his later writings, and, at length, he admits that a "germ" need not be an actual miniature of the organism ; but that it may be merely an " original preformation " capable of producing the latter. 3 But, thus denned, the germ is neither more nor less than the " particula genitalis " of Aristotle, or the " primordium 1 Considerations sur les Corps organists, cliap. x. 2 Bonnet had the courage of his opinions, an<l in the Palingenesie Philosophigue, pait vi. chap. iv. , lie develops a hypothesis which he terms "evolution naturelle;" and which, making allowance for his peculiar views of the nature of generation, bears no .small resemblance to what is understood by " evolution" at the present <l;iy : "Si la volonte divine a cree par un seul Acte 1 Universalite des f tres, d ou venoient ces plantes et ces animaux dont Moyse nous decrit la Production au troisieme et au cinquieme jour du renouvellemeut de notre rnonde ? " Abuserois-je de la liberte de conjectures si je disois, que les Plantes et les Animaux qui existent aujourd hui sont parvenus par une sorte d evolution naturelle des Etrea organises qui peuplaient ce premier Monde, sorti immediatemeut des MAINS du CUKATKUR? .... " Ne supposons que trois revolutions. La Terre vient de sortir des MAINS du CRKATEUB. Des causes preparees par sa SAGKSSE font developper de toutes parts les Germes. Les Etres organises comnien- cent a jouir de 1 existeuce. Us etoient probablemeut alors bien dif- ferens de ce qu ils sont aujourd hui. 11s I etoient autant que ye premier Monde differoit de celui que nous habitons. Nous mansions de moyens pour juger de ces dissemblances, et peut-etre que le plus habile Naturaliste qui auroit ete place dans ce premier Monde y auroit entiere- ment meconnu nos Plantes ct nos Animaux." 3 " Ce mot (germe) ne designers pas settlement un corps organise rlduit en petit ; il desiguera encore toute espece de priformation oriyiiielle dont un Tout organiquepeut risulter comme de son principle immtdiat." I aiingciiesie I hilosopliiqve, part x. chap. ii. vegetale" or "ovum" of Harvey; and the "evolution" of such a germ would not b3 distinguishable from " epigenesis." Supported by the great authority of Haller, the doctrine of evolution, or development, prevailed throughout the whole of the 18th century, and Cuvier appears to have substantially adopted Bonnet s later views, though probably he would not have gone all lengths in the direction of " emboitement." In a well-known note to Laurillard s J^loge, prefixed to the last edition of the Ossemens fossiles, the "radical de 1 etre" is much the same thing as Aristotle s "particula genitalis" and Harvey s "ovum." 4 Bonnet s eminent contemporary, Buffon, held nearly the same views w r ith respect to the nature of the germ, and ex presses them even more confidently. " Ceux qui ont cru que le cceur etoit le premier forme, se sont trompes; ceux qui diseut que c est le sang se trompent aussi: tout est forme en meine temps. Si 1 on ne consulte que 1 observation, le poulet se voit dans I osuf avant qui il ait ete couve." 5 " J ai ouvert une grande quantite d ceufs a diflerens temps avant et apres 1 incubation, et je me suis convaincu par mes yeux que le poulet existe en entier dans le milieu de la cicatrule au moment (ju il sort du corps de la poule. " 6 The "moule interieur" of Buffon is the aggregate of elementary parts which constitute the individual, and is thus the equivalent of Bonnct r. germ, 7 as defined in the passage cited above. But Buffon further imagined that innumerable " molecules organiques " are dispersed through out the world, and that alimentation consists in the ap propriation by the parts of an organism of those molecules which are analogous to them. Growth, therefore, was, on this hypothesis, partly a process of simple evolution, and partly of what has been termed syngenesis. Buffon s opinion is, in fact, a sort of combination of views, essentially similar to those of Bonnet, with others, somewhat similar to those oi 1 the " Medici " whom Harvey condemns. The "molecules organiques" are physical equivalents of Leib nitz s "monads." It is a striking example of the difficulty of getting people to use their own powers of investigation accurately, that this form of the doctrine of evolution should have held its ground so long; for it was thoroughly and completely ex ploded, not long after its enunciation, by Caspar Frederick Wolff, who in his Theoria Generationis, published in 1759, placed the opposite theory of epigenesis upon the secure foundation of fact, from which it has never been displaced. But Wolif had no immediate successors. The school of Cuvier was lamentably deficient in embryologists; and it was only iu the course of the first thirty years of the pre sent century, that Prevost and Dumas in France, and, later on, Dollinger, Pander, Von Bar, Rathke, and Remak in Germany, founded modern embryology; and, at the same time, proved the utter incompatibility of the hypothesis of evolution as formulated by Bonnet and Haller, with easily demonstrable facts. Nevertheless, though the conceptions originally denoted by "evolution" and "development" were shown to be untenable, the words retained their application to the process by which the embryos of living beings gradually make their appearance; and the terms "Development," 4 "M. Cuvier considerant que tons lc-s etres organises sont derives de parens, et ne voyant dans la nature aucune force capable de produire 1 oiganisation, croyait a la pre-existence des gernies ; non pas a la pre- existence d un etre tout forme, puisqu il est bien evident qne ce n est que par des developpemens successifs que 1 etre acquiert sa forme ; niais, si Ton pent s exprimer ainsi, a la pre-existence du radical de 1 etre, radical qui existe avant que la serie des evolutions ne commence, et qui remonte certainement, suivant la^ belle observation de Bonnet, a plusieurs generations." Laurillard, Eloge de Cuiicr, note 12. 5 Ilistoire Naturelle, torn. ii. ed. ii. 1750, p. 350. 6 Ibid., p. 351. 7 See particularly Buffon, I.e. p. 41.
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