(Haller, Bonnet) and sometimes was broken. At that time 

 the idea of "the steps" was combined with the epigenetic 

 opinions on development (Radishchev) . 



The preformation of the eighteenth century heavily 

 leaned on two trends developed in the previous one hundred 

 years, concerning the bearer of the preformation — whether 

 spermatozoid or ovum. The supporters of spermatozoid 

 preformation were called animalculists (from animalculum = 

 animals, which the spermatozoids were called; these were 

 discovered in the seminal fluid by Ham and Leeuwenhoek 

 in 1677) . The supporters of preformation of the embryo in 

 the ovum were named the ovists;" these latter were more 

 numerous and include Haller, Bonnet, Vallisneri and others. 



If Vallisneri, as fairly suggested by A. D. Nekrasov, 

 is considered not more than a compiler, Albrecht von Haller 

 and Charles Bonnet were undoubtedly the original investiga- 

 tors. Their theoretical opinions on the development of the 

 organism did not rise, however, above the level of 

 Vallisneri' s presentations. 



Haller, who was an early supporter of epigenesis, 

 arrived at the idea of preformation from his own investiga- 

 tions of chick development. (16) These investigations do 

 not give any proof of pre-existence of the organism in the 

 egg, because Haller assumed a close connection of the chicken 

 embryo with the yolk and erroneously took the yolk sac for 

 the yolk membrane. Consolidating the position of preformation, 

 Haller took this doctrine up the hypothesis of "enclosing" (17) 

 and denied the possibility of the new formation in embryonic 

 development. Haller' s aphorisms, "No epigenesis exists" and 

 "No part of the animal appears before the others, and all are 

 simultaneously created," were extremely popular in the second 

 half of the eighteenth century. Haller formulated his 

 discussions more cautiously than Bonnet, and he was willing 

 to discuss the arguments for epigenesis; he positively 

 evaluated wolff's dissertation although he did not agree 

 with his final conclusions. 



For details about the animalculists and ovists of the 18th 

 century see the books of A. D. Nekrasov, FERTILIZATION 

 IN THE ANIMAL KINGDOM (1930) and Joseph Needham, 

 HISTORY OF EMBRYOLOGY. 



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