SECT. 3] AND EIGHTEENTH CENTURIES 205 



of animals and plants, could treat the epigenesists as no better than 

 atheists. 



Spallanzani's views on embryology were largely drawn from his 

 study of the development of the frog's egg. Here he went far beyond 

 Bosius, but, in spite of many careful observations, he thought he saw 

 the embryo already present in the unfertilised ova. This led him to 

 claim that amphibia ought to be numbered among viviparous 

 animals. His principal step forward was his recognition of the 

 semen as the actual agent in fertilisation on definite experimental 

 grounds — the narrative of his artificial insemination of a bitch 

 is too famous to quote; he said it gave him more intellectual satis- 

 faction than any other experiment he had ever done. This demon- 

 stration finally disposed of the aura seminalis which Harvey had 

 found himself obliged to adopt on the grounds of his dissections on 

 does. Curiously enough Spallanzani never convinced himself that 

 the spermatozoa themselves were the active agents. 



3-13. Preformation and Epigenesis 



Of all the preformationists Charles Bonnet was the most theoretical. 

 He was an adherent of that way of thinking mainly on the theoretical 

 ground that the organs of the body were linked together in so intimate 

 a manner that it was not possible to suppose there could ever be a 

 moment when one or two of them were absent from the ranks. "One 

 needs", he said, "no Morgagni, no Haller, no Albinus to see that 

 all the constituent parts of the body are so directly, so variously, so 

 manifoldly, intertwined as regards their functions, that their relation- 

 ship is so tight and so indivisible, that they must have originated all 

 together at one and the same time. The artery implies the vein, 

 their operation implies the nerves which in their turn imply the 

 brain and that by consequence the heart, and every single condition 

 a whole row of other conditions." Bonnet compared epigenesis to 

 crystal-growth in which particles are added to the original mass 

 independently of the plan or scheme of the whole, i.e. in opposition 

 to the growth of an organism, in which particles are added on only 

 at certain places and certain times under the guidance of "forces de 

 rapport". Przibram has recently discussed the question of how far 

 such a comparison is admissible, but, in Bonnet's time at any rate, 

 it became very famous. Bonnet made reference to Haller's discovery 

 of the intimate relationship between embryo and yolk as evidence 



