2o6 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



for his theory. The embryo begins, according to him, as an exceedingly 

 fine net on the surface of the yolk, fertilisation makes part of it beat 

 and this becomes the heart, which, sending blood into all the vessels, 

 expands the net. The net or web catches the food particles in its 

 pores, and Bonnet supposed that, if it were possible to abstract all 

 the food particles at one operation from the adult animal, it would 

 shrivel and shrink up into the original invisible web from which it 

 originated. 



Bonnet was no more afraid of the emboitement principle than was 

 Haller; indeed, he called it "one of the greatest triumphs of rational 

 over sensual conviction". Many of his arguments were reproductions 

 of Haller's, and he says in his preface that he had written his book 

 some time before Haller's papers on the chick appeared, but then, 

 finding his own views confirmed by the more experimentally founded 

 ones of Haller, he determined to publish what he had set down. Thus 

 in one place he says, " I shall be told, no doubt, that the observations 

 on the development of the chick in the tgg and the doe in the maternal 

 uterus make it appear that the parts of an organised body are formed 

 one after another. In the chick for instance it has been observed that 

 during the early part of incubation the heart seems to be outside 

 the animal and has a very diflferent form to what it will have. But 

 the feebleness of this objection is easy to apprehend. Some people 

 wish to judge of the time when the parts of an organised body 

 begin to exist by the time when they become visible to us. They 

 do not reflect that minuteness and transparency alone can make 

 these parts invisible to us although they really exist all the 

 time". 



Bonnet was therefore what might be called an " organicistic pre- 

 formationist", for his objection to epigenesis lay in the fact that it 

 apparently did not allow for the integration of the organism as a 

 whole. His mistake was that he assumed the capacities of the adult 

 organism to be present all through foetal life, whereas the truth is 

 that they grow and differentiate in exactly the same way as the 

 physical structure itself does. Bonnet's philosophical position, which 

 has been analysed by Whitman, seriously contradicts the generalisa- 

 tion of Driesch that all the epigenesists were vitalists and all the pre- 

 formationists mechanists. For Bonnet an epigenetic and a mechanical 

 theory were one and the same; he hardly distinguished, as Radl 

 says, between Descartes and Harvey; and it was just the neo-vitalistic 



