284: EVOLUTION IN BIOLOGY. 



branche ; * while, in the middle of the eighteenth cen- 

 tury, not only speculative considerations, but a great 

 number of new and interesting observations on the phe- 

 nomena of generation, led the ingenious Bonnet, and 

 Ilaller, f the first physiologist of the age, to adopt, ad- 

 vocate, and extend them. 



Bonnet affirms that, before fecundation, the hen's 

 egg 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 conse- 

 quence of this intussusceptive growth is the " develop- 

 ment " or " evolution " of the germ into the visible bird. 

 Thus an organised individual (tout organise) " is a com- 

 posite body consisting of the original, or elementary, 

 parts and of the matters which have been associated 



teur de la ' Recherche de la Verite,' M. Regis, M. Hartsoeker, et d'autres 

 habiles homines n'ont pas ete fort eloignes de ce sentiment." Leibnitz, 

 " Systeme nouveau de la Nature," 1695. The doctrine of " Emboitement " 

 is contained in the "Considerations sur le principe de vie," 1705; the 

 preface to the " Theodicee," 1710; and the "Principes de la Nature et de 

 la Grace " ( 6), 1718. 



* " II est vrai quo la pense"e la plus raisonnablc et la plus conforme a 

 1'experience sur cette question tres difficile de la formation du foetus ; c'est 

 que les enfans sont deja presque tout formes avant meme 1'action par la- 

 quelle ils sont census ; et que leurs meres ne font que leur donner 1'accrois- 

 sement ordinaire dans le temps de la grossesse." " De la Recherche de la 

 Verite," livrc ii. chap. vii. p. 334, 7th ed., 1721. 



f The writer is indebted to Dr. Allen Thomson for reference to the evi- 

 dence contained in a note to Haller's edition of Bocrhaave's " Praelectiones 

 Academicoe," vol. v. pt. ii. p. 497, published in 1744, that Haller originally 

 advocated epigenesis. 



