The pronephros of Chryseiiiys inarginata. 37 



(5,6 — 5,11 Nephrostome at 5,6 and 5,7; tubule opens into 

 X I duct at 5,11 ; probably the rudiments of a 



I nephrostome also at 5,12. 



1 5,14— 5,21 Tubule with openings into nephrotome at 5,14, 

 -^^ I 5,16 and 5,21, and into duct at 5,21. 



Behind this region the tubules appear to be undoubtedly meso- 

 nephric, and open at 5,25, 5,28, 5,33, 5,36 into the nephrotome 

 and duct. 



The pronephric duct fuses with the gut wall at and after 8,35. 

 (See Plate 2, 3 and 4 Figs. 27 to 53.) 



Embryo N. 



Length measured along curved axis of body = 6 mm. (approx.). 



Stained in Geenachek's Boraxcarmine. 



Heart twisted. Tail distinct and tapering. Counted 23 -|- proto- 

 vertebrae. Mounted upon 3 large slides having respectively 102, 

 96 and 126 sections. 



Owing to the body-flexure it is now useless to attempt to de- 

 termine the segments of tlie body in which the kidney tubules occur 

 in this and subsequent embryos. This embryo (N) is about the same 

 age as, or a little older than, the preceding embryo. 



Gut begins 1,33. Neurenteric canal 3,110 — 3,116. Heart begins 

 1,59; ends 1101. 



The pronephric duct has a solid connection with the gut on 

 both sides from 3,79 to 3,82. 



In this embryo the position of tlie kidney is: 



Left side. 

 VI? Glomus begins 1,61. 



[1,63—1,69 Signs of a rudimentary tubule which does not 

 ^1 reach the duct. 



I 1,70 I Nephrostomes of two tubules which open 



VIII I At ^^^^1 ^74^ Y5 j into the duct at 1,72. 



I 1,84 and 1,85. Nephrostome at 1,84; tubule opens into the 

 ^^ ( duct at 1,85. 



1 1.93—1,99 Nephrostome at 1,94 — 1,96 of a tubule opening 



. j into pronephric duct at 1,99. 



X I 2,2 — 2,5. The nephrostome (2,2 — 2,4) of a tubule which opens 



j into the lower end of the open nephrotome; 



( the tubule joins with the duct at 2,4 and 2,5. 



