iv] MULTIPOLAR SPINDLES 57 



with this conclusion, which was mentioned in a former 

 chapter when the size-relations of nucleus and cytoplasm 

 were being considered. In an egg which, in consequence of 

 abnormal conditions, receives two spermatozoa, each may 

 give rise to two centrosomes, so that four centrosomes may 

 exist together, and cause the production of a quadripolar 

 spindle. The result of this is that the combined egg and 



FIG. 6. Tripolar and quadripolar spindles in segmenting Echinoid 

 eggs, after GRAY (1913). 



sperm nuclei divide simultaneously into four. Usually the 

 four daughter-nuclei contain unequal numbers of chromo- 

 somes, and in consequence are of different sizes, and it is 

 found that the cell divides in such a way that the volume 

 of cytoplasm around each nucleus is roughly proportional 

 to the volume of the nucleus. In this case, therefore, the 

 plane of division seems to depend primarily on the nucleus 



