The pronephros of Chrysemys marginata. 



9 



is indented: this fact is important when we have to consider the 

 close relation which exists temporarily between ectoderm and the 

 backward prolongation of the kidney rudiment at a later embryonic 

 stage. 



5. The incipient traces of the urinary organ are observable as 

 far forward as the anterior region of segment III (left side) and 

 the posterior region of segment II (right side). 



Left side 



Embryo B. 

 Body begins 1,1 



Right side 



mf 



IV 



?VII I 



1,16 



1,31 



Foregut ends 



2,10 



2.25 



3,4 



3.19 



! ear 



I 



\ in 

 i 



!iv 



;vi 



I VII? 



3.34 



4,13 



neurenteric ( 

 canal \ 4,28 



5,5 



(Scale = 3 sections 

 to a division) 



