266 



G. R. DE BEER 



(^r— - 



5.(./i. 

 Petromyzon planeri. Embryo 10 mm. long. 



O.L.. 



Hd 



O.ch 



Ui '... 



PN 



Petromyzon planeri. Embryo 15 mm. long. Appearance of 

 neuroglia thickening in the wall of the infundibulum. 



