Text-fig. 17. 

 L.t. 



M.$ 



K.2 



Sh.gld. 



Ac 



Section tln-ough the same region of an embryo in the same stage 

 as m fig. 4 o± PL 22, showing the first signs of the accumulation 

 ot mesoderm cells m which the coelom is formed at a later 



stage. 



Text-fig. 18. 



R.l. 









-^* 





cr^" 



' ' I 



A.c. 



Section through approximately the same region of a slightly older 

 embryo. The coelom is now a definite cavity Ijounded by the 

 mesoderm cells. The secondary kidney is here shown cut across 

 its long axis. 



