later stage of egg development in other animals. With the 

 transference of the egg nucleus comes the formation of the 

 central cavity of the yolk and its canal. In the frog egg, 

 where the transference of the embryonic vesicle occurs late, 

 Baer observed it with greater distinctness than in the bird's 

 egg. 



After copulation, the cicatrice is ruptured and the 

 yolk falls from the cavity of the capsule. For the release 

 of the yolk, copulation is not necessary, but it stimulates 

 this process. Many authors after Baer described the dis- 

 appearance of the embryonic vesicle upon maturation of eggs 

 of many types of animals. But only after the investigation 

 of N. A. Warnek (see Chapter 25) did this phenomenon become 

 connected with maturation division and the formation of the 

 polar bodies. Baer considered the appearance of the rudiment 

 (KEIM) from the rudiment layer a direct consequence of 

 fertilization, and without fertilization the rudiment is 

 not formed . 



Describing the further formation of the egg, which is 

 already occurring in the oviduct (§ 4) , Baer first considered 

 the organization of the sexual conducting routes and described 

 the structure of the funnel, especially the oviduct and uterus, 

 from which a narrow passage leads to the cloaca. The pressing 

 of the yolk ball by the funnel and its passage along the 

 oviduct is accomplished by active movement of the latter; 

 hence the yolk, passing by the oviduct, turns around the 

 longitudinal axis so that the rudiment layer always remains 

 on one side. After passage of the egg, the walls of the 

 oviduct produce albumen, which gradually envelops the yolk 

 ball. The shell membrane forms, in Baer's opinion, from the 

 surface layer of the albumen, because the latter rolls up 

 when the egg reaches the uterus. In this division of the 

 oviduct the "hail-stones" (HAGELSCHNURE) and the shell are 

 formed. In the uterus the egg remains nearly a day. Concern- 

 ing the formation of the rudiment, Baer assumed that it 

 develops from the content of the embryonic vesicle, indicating 

 a contradiction because there is no rudiment in the unfertilized 

 eggs even though the embryonic vesicle may have ruptured even 

 without fertilization. 



Not deciding beforehand the question of whether the embryo 

 is produced only from the egg nucleus, Baer accorded the latter 



375 



