ORIGIN OF MYCETOCYTES IN PSEUDOCOCCUS. 287 



and second polar bodies. The first difficulty arises in determining 

 the number of divisions to which the polar nucleus is subjected. 

 It seems certain that at least two divisions take place regularly 

 and that they are always normal. In some cases, the 4 nuclei or 

 polar nucleus derivatives resulting from these two divisions 

 certainly undergo a third division. But whether this last divi- 

 sion occurs in every egg is not so certain. If so, there will then be 

 8 polar nucleus derivatives at the periphery of the egg (Fig. 4-7 a). 



Almost the same difficulties are encountered in determining the 

 number of divisions that the fertilization or zygote nucleus under- 

 goes, before the resultant cleavage cells take up their migration 

 to the periphery to establish the blastoderm. Typically there 

 appear to be about 32 cells in the interior of the egg when the 

 migration begins. 



It will be apparent that there is a distinct variation in the rate 

 of division of polar nucleus derivatives and cleavage cells respec- 

 tively. While the polar nucleus is undergoing at most 3 divisions, 

 the fertilization nucleus undergoes approximately 5. The result 

 of this is that while all the nuclei of each type taken by itself are at 

 about the same stage of division, they may not be at all synchron- 

 ous with the division stages of the other type. It is this condition 

 that lies at the bottom of the difficulty in determining the number 

 of divisions that the nuclei in question undergo before the process 

 of fusion is begun. Thus in one egg, there are 8 polar nucleus de- 

 rivatives, all in slightly varying stages of telophase, and still 

 connected in pairs by spindle fibers (Fig. 7). The cleavage cells 

 of this egg have begun the peripheral migration, but none have 

 yet reached the edge. It can be assumed that here 8 polar nucleus 

 derivatives will be involved in the processes of fusion to follow. 

 In contrast with this is another egg in which there are only 4 

 polar nucleus derivatives. The chromosomes are in the final 

 stage of condensation but the nuclear walls have not yet been 

 broken down. The cleavage cells, present in about the same 

 number as in the previously mentioned egg (32), are again in the 

 stage of migration, and one has actually come in touch with one 

 of the polar nucleus derivatives at the periphery. This cleavage 

 cell like its sister cells is in the resting phase. The question there- 

 fore arises whether the polar nucleus derivative will complete its 



