44 T. H. BUBLEND, 



Embryo R. 



The pronephros presents a condition similar to that found in 

 embryo Q, — the embryos not differing very much in age. 



Embryo S. 



This embryo was somewhat older than the preceding ones. 



In it the pronephros appears as a degenerate much reduced 

 structure at the front end of the mesonephros, into which it gradually 

 merges. The glomus is very much reduced. 



Embryos 0— S 



show the pronephros in various phases of degeneration. 



The above description of them has been given in order to illus- 

 trate important changes in the late pronephros. 



These changes may be summarized as follows: 



1. The pronephric tubules undergo great increase in length ac- 

 companied by complicated twisting. 



2. There is evidence of subdivision of the original pronephric 

 nephrostomes so that the tubules come to have more than one coe- 

 lomic (or nephrotomic) opening. 



3. The changed relations of the vascular supply and the grada- 

 tional change from the pronephric to the mesonephric condition 

 is apparent from an examination of Textfig. M. 



These drawings are diagrammatic representations (traced in 

 outline with the aid of a camera lucida) of successive sections taken 

 through the front region of the kidney of embryo P. 



4. The tendency of the glomus to become subdivided; also the 

 tendency of the branches of the glomus to fuse with the somatic 

 mesoderm in the region of the nephrostomes whereby the latter no 

 longer open into the coelom direct. 



The further discussion of the later condition of the pronephros 

 will be deferred until the vascular supply in all these embryos has 

 been dealt with. 



The development of the Pronephric duct in Chrysemys 



tnarginata. 



Felix speaks of the pronephric duct (primäre Harnleiter) as 

 composed of the following parts: 



