507 



pr. d. 



sp. cd. 



Fig. IX. 



sp. cd. 



pr. d. 



Fig. X. 



each side). In the Dogfish the change was simplified owing to the 

 insignificance of a vascular glomus. 



See figs. XI, XII and XIII. 



The pronephros in Chrysemys is thus confined to segments YII 

 to X: in rather late embryos it appears as a number of tubules (from 

 6 to 8) opening at one end into the extreme anterior region of the 

 coelom and at the other into the pronephric (segmental) duct. 



The vascular glomus also remains until a comparatively late'em- 

 bryonic stage as a much broken-up mass of tissue around the openings 

 of, and on the inner side of the pronephric tubules. 



