372 



BERTRAM G. SMITH 



Fig. 15 Diagrams showing the relation between the direction of the first 

 cleavage furrow and the median plane of the gastrula in forty-two eggs of Crypto- 

 branchus allegheniensis. The vertical line indicates the direction of the first 

 cleavage furrow, which was marked with Nile-blue sulphate; the arrow, pointing 

 anteriorly, indicates the direction of the median plane of the gastrula. 



