438 



INTRODUCTION TO CRAN1ATA 



[CH. 



2 1 



FIG. 216. Illustrating the development of 

 systems in Craniata. 



A. 



The pronephros in functional activity, the mesonephric tubules being 

 formed. B. The pronepbros degenerating, the mesonephros in func- 



tional activity. C. The mesonephros connected with the genital 



organs by vasa efferentia in its anterior portion, the pelvis of the meta- 

 nephros and the metanephric tubules being formed. D, E, represent the 

 condition which is found in the higher Craniata. D. The condition in 

 the female. The mesonephros connected with the ovary by vasa efferentia 

 and in process of degeneration disconnected from the mesonephric duct. 

 The metanephros fully formed and also the oviduct. E. The 



condition in the male. The capsules of the mesonephros have disappeared. 

 The metanephros is fully developed, the oviduct is vestigial. F. The 



condition in the embryo Elasmobranch. The mesonephros is connected by 

 vasa efferentia to the genital organ. The oviduct is arising by a splitting 

 of the longitudinal duct. G. The condition in the female Elasmobranch, 

 the hinder portion of the mesonephric duct alone persists and receives the 

 metanephric tubules. The oviduct is separated from the longitudinal 

 kidney duct. H. The condition in the male Elasmobranch. The 



mesonephros is connected with the testes, the oviduct is vestigial. 



