The pronephros of Chrysemys marginata. 43 



Embryo P. 



This embryo was about the some age as embryo 0. The con- 

 dition of the kidney is very similar to that of the last-mentioned 

 embryo, and the gradual transition from pronephros to mesonephros 

 is shown in Textfig. M. 



The glomus also is seen in the process of change to form the 

 glomeruli of the mesonephros. 



Stained with Ehelich's Haematoxylin and mounted upon 8 slides 

 having respectively (52, 49, 52, 52, 52 . . .) sections. 

 Left side. — Glomus begins 3,11. 



1st tubule (degenerate) nephrostome 3,21 — 3,24 

 2iicl tubule has nephrostome . . . 3,28—3,31 



3rd 3,34—3,35 



3,44 and 3,45 \ 

 3,49 and 3,50 j 



5th . . ^'^ 1 

 4,9 —4.11 / 



6th 4,15—4.18 



7th 4,21-4,23 X 



and etc. J 

 Right side. — 

 Glomus begins 3,12. 



Nephrostomes at 3,26 ; 3,27 ; 3,33 ; 3,37 ; 3,41 ; 3,47 ; 4,2, 4,5 etc. 

 I have not yet determined whether the last two or three ne- 

 phrostomes open into closed coelomic spaces or not: the distinction 

 between a pronephric and a mesonephric tubule in this region is 

 difficult to define. In fact one may safely say that to draw a hard 

 and fast line between posterior pronephric tubules and anterior 

 mesonephric tubules in this and similar Chrysetnys embryos is im- 

 possible. 



Embryo Q. 



Stained as before with Haematoxylin ; mounted upon slides each 

 having 4 rows of 13 sections. 



Kidney and glomus first cut across on each side at 3,48. 

 Nephrostomes on left side at 4,10?; 4,11; 4,20; 4,26?; 4,29; 

 4,34; 4,38; 4,46; 4,51 etc. 

 and on right side at 4,13; 4,20; 4,27 (?); 4,30; 4,39; 

 4,47; 5,2 etc. 



