No. 6.] AMERICAN MORPHOLOGICAL SOCIETY. 349 



normally fertilized eggs, but in many cases complete cyto- 

 plasmic division does not occur until after two or more nuclear 

 divisions. Thus arise some of the forms of multiple cleavage 

 observed by Morgan and Loeb. If cytasters be present, one 

 or more of them may participate in the nuclear division, thus 

 forming triasters, tetrasters, etc. ; but such eggs are probably 

 incapable of producing an embryo. When the cytasters do 

 not establish a connection with the chromosomes, they never- 

 theless form, in many cases, ineffective centers of cytoplasmic 

 division, i.e., cleavage furrows appear between them but after- 

 wards fade out. Apparently strong evidence was, however, 

 obtained that in some cases complete division may occur 

 around asters unconnected with nuclear material. In any case 

 the cytasters persist for some time and may progressively mul- 

 tiply by division. The first division actually observed takes 

 place nearly synchronously with that of the cleavage asters, 

 at a time when the daughter-nuclei have been formed and are 

 rapidly enlarging. Division of the asters is in both cases pre- 

 ceded by a great reduction of the astral rays, leaving the clear 

 hyaloplasmic central mass surrounded by only short irregular 

 rays, and at the same time the aster migrates out towards 

 the periphery of the egg. The mass then draws apart into 

 two, and recrudescence of the rays from the two centers ensues. 

 A discrepancy, not yet fully cleared up, lies in the fact that, 

 although the cytasters divide synchronously with the cleavage 

 asters, they have not been observed in the living eggs to divide 

 at the time the dicentric nuclear figure is first formed ; but the 

 study of sections indicates that this is probably owing to a gap 

 in the observations. The cytasters ultimately disappear. 



Asters are formed also in enucleated fragments, obtained by 

 shaking the unfertilized eggs into pieces, and such asters may 

 also progressively divide, though no case was observed of 

 cleavage, or even an attempt at cleavage, in such fragments. 

 Sections show that all the asters, whether cytasters or nuclear 

 asters, or those formed in enucleated fragments, contain cen- 

 trosomes which have the typical staining capacity and granular 

 structure observed in normally fertilized eggs. In the cytas- 

 ters, however, they are usually smaller than in the nuclear 



