368 



BERTRAM G. SMITH 



2. Constriction with a silk thread. Shortly after the appearance 

 of the first cleavage furrow, the accessory egg envelope was 

 removed and a silk cord tied around the egg in such a manner as 





2' 



Figs. 4 to 7 Surface views of the upper hemispheres of four eggs of Crypto- 

 branchus allegheniensis in early cleavage stages, showing the biradial character 

 of the cleavage pattern. Figs. 4 and 5, stage 4; fig. 6, stage 5; fig. 7, stage 6. 

 The figures were drawn with the aid of a camera lucida. X 7. 



to constrict it slightly in the direction of the first cleavage furrow. 

 The blastomeres were by no means entirely separated, and the 

 egg developed as a whole; the device served merely to mark the 

 direction of the first cleavage furrow. The operation is a delicate 



