The pronephros of Chrysemys marginata. 15 



that the general coelom does not approach so near to the proto- 

 vertebrae in segment VIII as it does in segment VI. At 4,32 and 

 4,33 the rudiment consists of flattened cells extending between 

 ectoderm and mesoderm almost up to the spinal cord. From 4,33 

 caudalwards the rudiment takes the form of a solid cord of 

 cells free from ectoderm and mesoderm. The cord ends at 4,45 as 

 a few (two or three) cells apparently derived from the neighbouring 

 mesoderm. 



On the right side the kidney rudiment extends over segments 

 VI, VII and VIII. It is free — as a solid duct — from the beginning 

 of segment IX to the middle of X. 



Embryo E. 



Stained in Grenacher's Boraxcarmiue for 49 hours. This 

 embryo, slightly curved, was 3,5 — 4 mm. in length. 



Sectioned, and mounted on 6 slides upon which were 41, 45, 44, 

 45, 47 and 48 sections respectively. 



Body begins 1,1. 



