248 II. M. KINGERY. 



part of the egg-cell was without any nuclei as a result of an in- 

 complete scattering of the chromosomes. The result of this 

 breaking up of the oocyte is that there are formed a number of 

 small "cells," some with several nuclei, some with one, and some 

 with none, so that the oocyte has the appearance of a "morula." 

 The fact that some "cells" have nuclei and others have not, is 

 due to the uneven distribution of the chromosomes in the cyto- 

 plasm of the oocyte when the spindle breaks down. In general, 

 the "cells" containing large nuclei, or a group of nuclei, are 

 larger than those with one nucleus or none. However, a definite 

 or effective control over this fragmentation is apparently lacking. 



Several authors, Newman among others, have described cells 

 in this "morula" stage which have spindles in them, and state 

 that these are cleavage spindles and that therefore this is a 

 case of parthenogenetic cleavage. It is more probable, however 

 that in such cases the cell containing the spindle is the first 

 polar body, which, as noted above, occasionally forms a spindle, 

 and which may in rare instances divide. In the white mouse no 

 spindle was found in any of the cells of this "morula" stage. 



In the cells of the "morula," and sometimes in the oocyte 

 before it has fragmented, are frequently found crystalloid bodies 

 the nature and origin of which are unknown. Possibly they are 

 a product of the degenerative changes in the egg-cell. Fat 

 granules are found in the oocytes in increasing numbers as 

 degeneration goes on. 



In a few instances the oocyte is found to have formed two cells 

 of nearly equal size, each containing a nucleus. Van der Stricht 

 describes such cases in the bat and states that each cell may 

 divide again, and each of the four cells thus formed may also 

 divide. The formation of two such equal cells may be explained 

 on the grounds that the scattered chromosomes were arranged 

 in two groups and formed two nuclei; the oocyte then broke up 

 into two fragments of equal size. Such an egg-cell is shown in 

 Fig. 10, with the first polar body also present; but the two nuclei 

 are not equal in size, nor normal in appearance. In fact, one is 

 apparently little more than a vacuole. 



The fate of the "morula" may be briefly described. The 

 zona pellucida usually persists as a thick transparent membrane 



