BILATERALITY IN CRYPTOBRANCHUS 383 



changes within; the outer layer of cells is becoming epithelial in 

 character. 



2. Relation to the plane of first cleavage. In the following 

 experiments the first cleavage furrow was identified in the vegetal 

 hemisphere only. 



Thirteen preserved eggs in stages 5 to 8, inclusive, were spht 

 with a razor along the plane of first cleavage. In three eggs the 

 first cleavage furrow coincided with the axis of excentricity as 

 revealed by the internal structure, in seven eggs the first cleavage 

 furrow was obHque to the axis of excentricity, and in the three 

 remaining eggs the first cleavage furrow extended at right angles 

 to it. So far as they go, these results indicate that there is no 

 fixed relation between the plane of first cleavage and the axis 

 of excentricity in the internal structure. 



The matter was further investigated by means of serial sections. 

 Eleven eggs in stages 5 to 8, inclusive, were cut into sections par- 

 allel to the first cleavage furrow; in nine of these eggs the merid- 

 ional sections showed unequal development of the micromeres 

 on opposite sides of the polar axis, while in the two remaining 

 eggs the meridional sections gave no evidence of such differentia- 

 tion. This result considered alone might be taken to indicate a 

 tendency for the axis of excentricity to coincide with the plane 

 of first cleavage; but this conclusion is nullified by the results of 

 the preceding test, also by the one which follows : of eleven eggs 

 in stages 5 to 8, inclusive, sectioned at right angles to the first 

 cleavage furrow, six showed excentricity in the meridional sec- 

 tions, while in five the meridional sections were lacking in this 

 feature. 



F. The bilateral syinmetry of the superficial cleavage pattern in the 

 lower hemisphere of the late hlastula 



In the late blastula (stages 9 and 10) bilateral symmetry is 

 usually recognizable in the cleavage pattern of the lower hemi- 

 sphere. The vegetal pole, marked by the point of intersection of 

 the first and second cleavage furrows, is excentrically situated 

 within the area occupied by the macromeres: a more rapid 

 multiphcation of cells has occurred on one side of the egg, where 



