g2 CHIM^ROID FISHES AND THEIR DEVELOPMENT. 



the yolk, and here at various points yolk nuclei are clustered, having evidently an 

 important physiological relation with the overlying blastoderm ; we note at a a 

 tongue of mesoblast cells which projects medianward; this occurs but in a few 

 sections, and evidently corresponds to the dark area noted in surface view; it 

 resembles, however, so closely the "lame intermediaire" (Swaen and Brachet) 



b b c 



■ he 



n K( '-^ 



'^m 



Figs. 71 F-I. (For description and lettering see page 81, A-E.) 



in the teleost, that, if for no other reason, we are led to suggest that it represents 

 the precocious beginnings of the excretory system. In e the notochord has sepa- 

 rated from the yolk, the gut lumen becomes narrowed, and lateralward the first 

 trace of a body cavity (dc) appears. We observe that the margin of the gut 

 passes directly into yolk-entoderm, the distinctness of its lower boundary having 



