BILATERALITY IN CRYPTOBEANCHUS 



369 



one, and even after it had been accomplished with every appear- 

 ance of success, the egg usually collapsed in a later cleavage 

 stage. Out of a considerable number of eggs treated in this way, 



Figs 8 to 11 Surface views of the lower hemispheres of four eggs of Crypto- 

 branchus allegheniensis, showing the biradial character of the cleavage pattern 

 Fig. 8, stage 5; fig. 9, stage 6; fig. 10, stage 7; fig. 11, stage 9. The figures were 

 drawn with the aid of a camera lucida. X 7. 



only nine lived to form gastrulae; the appearance of the lower 

 hemispheres of these eggs in the gastrula stage is shown in figure 

 14. It will be observed that in two of these eggs the median 

 plane of the gastrula coincides approximately with the plane of 



