330 EDWIN G. CONKLIN 



the further division of both cells, and there is no evidence what- 

 ever that the activating influence of the spermatozoon is due to 

 these granules. 



On the other hand many investigators have held that fertili- 

 zation is essentially a chemical process and that the activation 

 of the egg depends upon the introduction by the spermatozoon of 

 certain chemical substances which diffuse throughout the egg. 

 The observations recorded in this paper indicate that the sec- 

 ond or internal factor in normal fertilization is a non-diffusible 

 substance which is introduced by the spermatozoon, and they 

 strongly suggest, though they do not prove, that this factor is 

 the sperm centrosome, a position which Boveri has long main- 

 tained and which I have hitherto contested. 



5. Cleavage of eggs centrifuged during maturation stages (figs. 



33 to 58, 75, 105) 



If centrifuging ceases long enough before cleavage begins to 

 allow a return of the egg substances to their usual positions, the 

 cleavage will be absolutely normal, irrespective of where the 

 polar bodies may have been formed. Thus in figures 35 to 44, 

 47, 49 to 54 the cleavage is proceeding in a wholly normal man- 

 ner although one or both of the polar bodies were formed at a 

 distance from the animal pole, and in some instances even at the 

 vegetal pole (figs. 35, 36, 38, 39, 44, 105). In figure 40 the 

 effects of centrifuging persisted throughout the first cleavage 

 so that one of the daughter cells contains more cytoplasm and 

 less yolk than the other one, but such eggs may develop into 

 normal embryos, as I have shown elsewhere ('12). Even in 

 such eggs as those shown in figures 44, 45, 49 in which the vol- 

 ume of the 'polar body' may be greater than that of the 'egg,' 

 the cleavage of the latter is perfectly normal except for the 

 smaller size of the blastomeres formed and for alterations in the 

 relative quantities . of cytoplasm and yolk. In figure 44 the 

 giant polar body was formed at the vegetal pole which is still 

 marked by the protruding 'yolk lobe;' in figure 45 the giant 

 polar body lies at the animal pole and contains almost all the 



