Embryology. 119 



anything- but a metaphysical conception of develop- 

 ment. "Not only is there", he said, "a soul or vital 

 principle present in the vegetative part, but even before 

 this there is inherent mind, foresight, and understand- 

 ing, which, from the very commencement to the being 

 and perfect formation of the chick, dispose and order 

 and take up all things requisite, moulding them in the 

 new being, with consummate art, into the form and 

 likeness of its parents." 



It was well, indeed, that it should be pointed out 

 that development is a marvellous progressive process, 

 in the course of which the obviously complex arises 

 from the apparently simple, and the dissimilar or hetero- 

 geneous from the similar or homogeneous; but Harvey 

 overshot the mark, and made development miraculous. 

 It is a mistake, he said, to look for any "prepared 

 matter" in the egg; but by exaggerating this he left no 

 material basis for the inherent potentialities, and was 

 forced to conceive of them mystically. Moreover, he 

 was so far from understanding the egg, that he sug- 

 gested that the primordium might proceed from parents, 

 or arise spontaneously, or out of putrefaction. As 

 Huxley points out, Harvey believed in spontaneous 

 generation as firmly as Aristotle did. That he did great 

 service must be freely allowed, but there has been a 

 tendency to read the experience of the nineteenth cen- 

 tury into some of his sentences. 



Charles Bonnet (1720-1793) may be taken as the most 

 thoroughgoing representative of the preform ationist 

 school, whose erroneous doctrines greatly Bonnet and 

 inhibited the progress of embryological re- the Prefor- 

 search for more than a century. He was mationists - 

 the discoverer of the parthenogenesis of green-flies or 

 Aphides, and made many interesting concrete observa- 

 tions on polypes and worms, but after the failure of his 

 eyesight he became more exclusively a speculative 

 thinker. He pondered over the phenomena of genera- 

 tion and development, and ended, strange to say, by 

 virtually denying them both. His central idea was the 

 " preformation " or asserted pre-existence of the organism 

 and all its parts within the germ. Not that he supposed 



