The pronephros of Chrysemys margiuata. 



71 



Thus the structure of the right and the left kidney is not quite 

 identical, probably because the early development of the left kidney 

 proceeds for a time slightly in advance of that on the right side. 

 (see Tables of Embryo A — J). 



Price finds this condition in Myxinoids; also Felix (in Trout) 

 says the „Vornierenfalte" is slightly further forward on the right side 

 than on the left. 



2. The environmental variation in different regions 

 of the kidney. 



This variation can be traced to a slight rotation of the posterior 

 part of the pronephros (through an angle of 90^ approximately) 

 a much greater rotation of the mesonephros, and perhaps a still greater 

 twist for the metanephros. 



nep 



pr. (I 



pr. (I 



Textfig. D. 



Textfiff. E. 



Textfig. D. This diagram illustrates the relations to each other of coelora, 

 pronephric duct {pr. d) and tubule, and nephrotome {nejj) in the typical pronephric 

 condition. 



Textfig. E. This diagram illustrates the relations to each other of coelom, 

 pronephric duct {pr. d) into which passes a mesonephric tubule, and nephrotome 

 {nej)) in the mesonephric condition. The nephrotome region is now increased by 

 addition from the coelom, and the tubule opens into it. 



If then we could superimpose the positions of pro-, meso- and 

 metanephros, we should have pronephros most ventral, mesonephros 

 more dorsal, and metanephros most dorsal. This rotation will altect 

 the relative position of the pronephric duct, of the nephrostomes and 

 also the relative extent of the nephrotome. The diagrams in Text- 

 figs. D and E will make this more intelligible. 



The diagrams serve roughly to illustrate the changes described 

 above. Thus the pronephric duct in Fig. E is ventrolateral to the 

 tubule but doisal in Fig. D. The nephrostome in Fig. E opens into 

 the coelom direct wliilst in Fig. D it opens into the nephrotome, 



