Trying to clarify differences in development of different 

 animals, after detailed studies of chick embryology, Baer 

 turned to the study of development in invertebrates (isopodous 

 Crustacea, fresh-water and land molluscs) and also the lower 

 vertebrates (salamanders and frogs) . Baer wrote that "the 

 development of mammals had especially attracted me in regard 

 to the formation of the embryo itself as well as in regard to 

 the formation of the ovum. "4 



Working first on dog embryos and concentrating on the 

 early stages, Baer found very small semi-transparent vesicles 

 at the end of the oviducts. Under the microscope he could 

 detect rounded patches like that of the cock's trace, or 

 even smaller non- transparent rounded bodies of a granular 

 structure. "Thus I was led to find the ovum in this form as 

 it lies in the ovary before fertilization. In order to show 

 the importance of detecting the ovum, and in order to explain 

 why I could not start the investigation from this end, I am 

 allowing myself to refer to an older investigation. "^ 



Recalling the greatest anatomist and physiologist of 

 the eighteenth century, Albrecht von Haller, "a man of very 

 extensive knowledge and almost incomprehensible diligence," 

 Baer gave him credit for the investigation of heart and 

 vascular development and also for the study of the formation 

 of the skeleton. Haller' s study of development of the mammalium 

 ovum was unsuccessful, however; the investigations of Haller' s 

 student, the Russian physician J. C. Kuhlemann, conducted on 

 forty sheep, were also without results. 6 From these unsuccess- 

 ful investigations Haller concluded that "the formation of the 

 embryo takes place by coagulation of the fluid similar to 

 crystallization." This point of view persisted because of 

 Haller's almost unquestioned authority. 



In the 1820s, some investigators supported the previously 

 dominant idea that the origins of the primary ova are the 

 Graafian vesicles, which are entirely separated from the 



4. Ibid. , p. 421 (313) (306) . 



5. Ibid . , p. 422 (314) (307-308). 



6. Ibid . (308). Johann Christian Kuhlemann, DISSERTATIO 

 INAUGURALIS ANAT . -PHYSIOLOGICA EXHIBENS 

 OBSERVATIONES QUASDEM CIRCA NEGOTIUM GENERATIONS 

 IN 0VIBUS FACTAS (GSttingen, 1753), 60 p. 



287 



