Baer followed these phenomena also in frogs, snakes, 

 lizards, and birds. Although in fish he could not see 

 the early stages, he nevertheless claimed that they do 

 not constitute an exception. With Burdach, Baer observed 

 development extending from the abdominal side to the 

 spinal side in fish. These data Baer did not publish at 

 the time, but in 1824, under the heading, "What Did the 

 Notebooks of My Listeners Indicate?" (p. 24). 



The last paragraph (§ 6) is entitled "Comparison of 

 the Mammalian Ovule with the Ova of Other Animals." 

 Regardless of the differences seen in the ova of different 

 animals, there may also be significant similarities, 

 according to Baer. It is common, for example, for the 

 the ova of all animals to have a nucleus, or, as Baer 

 called it at that time, the Purkinje vesicle, named for 

 the famous Czech physiologist who discovered this 

 formation. Purkinje had described this formation in 

 his HISTORY OF THE BIRD'S EGG BEFORE INCUBATION, 

 which he dedicated to J. F. Blumenbach in connection with 

 his fiftieth anniversary of scientific activity (89) . 



Baer indicated that in all the ova investigated, the 

 Purkinje vesicle persists until the end of ovum development. 

 In mammals, the vesicle is included in the cumulus.. In the 

 deposited ova and in the ova located in the oviduct, he 

 never observed the follicle. According to Baer's observa- 

 tions, the follicle disappears earlier. For example, in 

 insects it disappears while it is still in the ovary. 

 Concerning the significance of the Purkinje vesicle, Baer 

 suggested that "the Purkinje vesicle is the effective part 

 of the ovum, by which the female faculty exerts its power, 

 as the male faculty resides in the male sperm." Concerning 

 the disappearance of the Purkinje follicle, which Baer 

 designated as "throwing out" and "dissolving," it is 

 "dependent upon the maturity of the ovum and upon the 

 irritation .... After fertilization the blastoderm 

 grows in the same place where the fluid content of the 

 follicle was poured off" (p. 29). 



Baer's words appear striking, especially his anticipa- 

 tion of the discovery of division of maturation and the 

 theory of polarity of the mature ova. Actually, the 

 expression "throwing out" of the Purkinje vesicle success- 

 fully describes the theory of separation of the polar bodies 



298 



