yolk. Baer indicated that in young ovarian ova the embryonic 

 vesicles are very large, and the bigger they become the less 

 the nourishing materials in the ovum. The details of this 

 controversy have not been established. 



Fertilization in fish takes place in the same way as in 

 the frog, at the moment of depositing the egg in the water; 

 in the viviparous fish, for example (Blennius viviparous) , 

 the four-eyed (anableps) and some silurids, the fertilizing 

 substance penetrates from the water into the genital orifice 

 of the female, and in some fish (Selachians), the fertilizing 

 substance is introduced there by the male, as occurs in 

 mamma 1 s . 



The structure of the ovum membrane of fish is variable; 

 it is a fine-grained or cartilaginous membrane (for example 

 in perch) or even shelled with four edges (egg-laying 

 selachians) . The rudimentary layer occupies a smaller space 

 on the surface of yolk in the fish which Baer investigated 

 than in amphibia, but relatively larger than in birds. Thus, 

 in Cyprinus blicoa.19 and pike the rudimentary layer occupies 

 a quarter of the yolk surface. In the center it is thicker 

 than at the edges, denser than the yolk and very transparent. 

 The embryonic vesicles in the deposited ova are not detected. 

 The rudimentary layer, according to Baer, after fertilization 

 is transformed into a rudiment without the preliminary division 

 of the yolk sphere, which he described in the amphibia. In a 

 footnote Baer referred to Baumgartner, who apparently saw 

 something similar in trout20. Although Baer could not directly 

 observe segmentation in the ova of fish, this did not prevent 

 him, as mentioned above, from recognizing that the process of 

 segmentation is a principal and universal phenomenon, with 

 which development begins. Later, referring to his work on fish 

 development, Baer remarked that he had not noticed divisions 

 taking place after fertilization. These divisions, he thought, 

 took place at night, and the protuberances on the surface of 



19. Cyprinus blicca , an old classification used by Baer, which 

 corresponds to the present name ABRAMIS (BLICCA) 

 BJORKNA, or ABRAMIS BRAMA. 



20. (Ed.: Baumgartner, "Beobachtungen viber die Nerven und 

 des Blut," p. 13.) . 



431 



