106 SCIENCE PROGRESS. 



tions of Swammerdam on the development of the frog tended 

 to confirm this view, but it is evident, from a perusal of 

 Swammerdam's work and a study of his drawings, that he 

 must have been strongly predisposed in favour of the evolu- 

 tion theory and have deceived himself in looking for the 

 " p reformatio," which he figures, though nothing like it 

 exists. 



This pre-existent miniature of the future animal was 

 supposed to nourish itself and grow, not in the way that we 

 now understand the process, but by taking in ready-made 

 material particles and packing them amongst the particles of 

 its own body, which was thereby caused to expand, unfold 

 and develop, just as gelatine is caused to swell up when 

 soaked in water. The pre-existent germ, it was supposed, 

 was stimulated to this course of development by fecundation, 

 by which process its latent or potential activities were 

 awakened, a conception which has been nearly faithfully 

 repeated within the last eighteen months. 1 



It must not be thought, however, that the evolutionists 

 of the eighteenth century were by any means unanimous in 

 accepting so very crude a theory. As physical and chemical 

 phenomena came to be better understood, so was this theory 

 seen to be more and more unsatisfactory, and Bonnet, who 

 accepted it with all its consequences in his earlier years, was 

 led in his later writings to make very considerable modifi- 

 cations in his views. He no longer regarded the germ as 

 an organised body reduced to miniature, but as "an original 

 preformation from which, as from its immediate principle, an 

 organic whole may be produced ". The conception of a 

 pre-existing entity in the germ, as thus expressed, is not 

 very different from the primordiwn vegetale of Harvey, and, 

 if allowance be made for the great difference that there is 

 between the knowledge of the minute structure of animal 

 tissues of to-day and that of a hundred years ago, it bears 



i 



Durch die Befruchtung vverden also nach meinen Auffassung zunachst 

 kinetische Energieen der direkten Entwickelung produziert oder ausgeldst. 

 W. Roux, Beitrage zur Entwickelungsmechanik des Embryo (Referate u 

 Beitrlige zur Anatomie tind Entwickelungsgeschichte, Bonnet and Merkel, 

 Anat. Hefte, bd. ii., p. 293). 



