§ 2 



SEXUAL CYCLE OF ZOARCES VIVIPARUS 



127 



pregnancy B 



mature ^ggs 

 — - medium - sized „ 

 small „ 



•"—corp.lutea „ 



2 3 months 



Fig. 84. Showing the relation between egg-development and corpus 

 luteum formation in Zoarces viviparus. 



from medium-sized ova, which in their turn were formed 

 from smaller ones. 



As in Rhodeus, the growth of the ova before ovulation is 

 completed in the space of 2 months at an accelerating speed 

 (Fig. 84). While the mature follicles are ovulating, the 

 medium-sized oocytes develop into pre-ovulation corpora 

 lutea, which remain in evidence during the whole of preg- 

 nancy, and finally evolve, after passing through the ingres- 

 sion-, functional- and regression-phases. Probably two 

 generations of corpora lutea make their appearance during 

 each pregnancy (Fig. 85). The fertilised oocytes of 20 mg 



Fig. 85. Showing the relation between egg-development and embryonal 

 development in Zoarces viviparus. 



