XL] EVOLUTION IN BIOLOGY. 277 



branche; 1 while, in the middle of the eighteenth 

 century, not only speculative considerations, but a 

 great number of new and interesting observations on 

 the phenomena of generation, led the ingenious 

 Bonnet, and Haller, 2 the first physiologist of the age, 

 to adopt, advocate, 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 con- 

 sequence of this intussusceptive growth is the " de- 

 velopment" or "evolution" of the germ into the 

 visible bird. Thus an organised 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 



1695. The doctrine of " Emboitement" is contained in the " Considera- 

 tions sur le principe de vie," 1705 ; the preface to the " Theodicee," 

 1710 ; and the " Principes de la Nature et de la Grace" ( 6), 1718. 



1 " II est vrai que la pensee la plus raisonnable 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 laquelle ils sont concus ; et que leurs meres DC font que leur donner 

 I'accroissement ordinaire dans le temps de la grossesse." "De la 

 Recherche de la Verite," livre ii. chap. vii. p. 334, 7th ed., 1721. 



2 The writer is indebted to Dr. Allen Thomson for reference to the 

 evidence contained in a note to Bailer's edition of Boerhaave's " Prselec- 

 tiones Academicae," vol. v. pt. ii. p. 497, published in 1744, that Haller 

 originally advocated epigenesis. 



