500 



CLAPP. 



[Vol. V. 



in the eight-cell stage differs considerably from what I have 

 observed. 



Fig. III. 4-6 have been introduced mainly for the purpose of 

 showing peculiarities of the eight-cell stage not shown by the 

 figures given by Dr. Brooks. The two- and four-cell stages are 

 much the same as in other fish eggs. In passing to the eight- 

 cell stage, the four cells elongate at right angles to the first 

 plane of cleavage, and the two planes of the third cleavage 

 divide these cells unequally, the four central cells being small, 

 while the end cells are much larger (Fig. III. 4-6). 





Fig. III. 



The bilateral symmetry is perfect with reference to either the 

 first or second line of cleavage, and it is so well marked in these 

 cases that it suggests the coincidence of the axis of the embryo 

 with the first cleavage plane. 



Fig. III. 3 is somewhat asymmetrical, while Fig. III. 8 shows 

 a remarkably symmetrical sixteen-cell stage. Fig. III. 7 shows 

 that stage in process of cleavage. 



Position of Adherent Embryos. 



In the paper referred to above, Dr. Ryder describes the 

 young adherent embryos as having their heads invariably 

 directed towards the opening of their retreat, and adds : " It 

 would seem that the direction from which the light comes has a 

 great deal to do in determining the direction of the axis of the 

 body of the future embryo." 



