156 Edward Hindle 



connected by spindle fibres, and therefore, in the case of multipolar, 

 mitoses, the egg may divide into as many cells as there are centres 

 of attraction Cytoplasmic cleavage does not necessarily follow a 

 multipolar mitosis, but the resulting nuclei may remain scattered 

 through the undivided cytoplasm of the egg and redivide, thus pro- 

 ducing a multinucleate cell. 



In addition to the formation of multipolar spindles the centres 

 of the cytasters may divide and thus produce a typical amphiaster 

 which may operate as a centre of cytoplasmic division independently 

 of the cleavage amphiaster. 



Occasionally a cell wall is developed between the two centres 

 of one of these cyt-amphiasters and thus an enucleated portion of 

 cytoplasm may become divided off from the main mass. 



In every case the formation of cytasters results in the production 

 of more or less irregular segmentation, or may completely stop 

 development. 



These cytasters resemble those described by WILSON in the eggs 

 of Arbacia after treatment with hypertonic salt solutions. The pheno- 

 mena observed by us in the eggs of S.purpuratus entirely support 

 his conclusions that there is no possibility of drawing any other 

 than purely an arbitarary distinction between cytasters and nuclear 

 asters in their relation to the nucleus and that the central bodies 

 of the cytasters are true centrosomes that are formed de nove in 

 the cytoplasm . 



Comparison of the Cytological Effects of Natural and Chemical 



Fertilization. 



In comparing these two processes it is necessary to avoid con- 

 sideration of those pathological phenomena that are always present 

 in a certain percentage of the chemically fertilized eggs. When the 

 sperm enters the ovum it introduces the exact amount of substances 

 (lysins, etc.) necessary to start normal development and there is little 

 chance of error. But when one attempts to imitate this process 

 chemically the possibilities of error are much greater. In the first 

 place the cytolytic substance may enter in excess; and similar 

 difficulties arise in the subsequent exposure of the eggs to the action 

 of the hypertonic solution, through the impossibility of ensuring 

 exactly the same exygen supply for all of the eggs. 



Therefore, the embryos that present pathological features should 



