Kyder.] [May 16, 



If these conclusions will hold universally, there is good ground for 

 believing that in the gradual evolution of protogyny the cytoplasmic field, 

 in which rapidly successive segmentations were possible, was also evolved. 

 If this is true, then sexuality itself arose as the consequence of protogyny 

 starting in parthenogenesis. The primary and secondary sexual charac- 

 ters of multicellular forms were also probably the outgrowth of secondary 

 and adaptive processes consequent upon the effects wrought as here sup- 

 posed through protogyny and the evolution of a large cytoplasmic field. 

 The origin of sex at any rate hinges upon the decision of how the dispro- 

 portion between the chrornatin and cytoplasm arose in the sexual pro- 

 ducts of the two sexes respectively. Upon its last analysis this problem 

 must resolve itself into purely physiological factors. 



These views are in accord with the first part of this paper , though it may 

 at first seem that the theory that the egg expels polar bodies because of its 

 specialized nature is not well founded. What there is in favor of such a 

 view is, that it harmonizes with the morphological and physiological data 

 of ovogenesis, and the conjugation of Infusoria. In any event, it is cer- 

 tain that if ova represent an incornpleted effort to produce spermatozoa, it 

 is very certain that they are specialized in so far as this effort has been 

 realized as supposed, in the formation of polar bodies and a large volume 

 of cytoplasm. 



Consequently ova may be regarded as incompletely differentiated sper- 

 matogonia. The undoing of this specialization whereby the egg becomes 

 the morphological equivalent of spermatozoon so far as its chromatin is 

 concerned brings us back to essentially the same basis as was followed in 

 the first part of this paper. 



Experimental evidence shows that the process of fertilization is self- 

 regulative and restricted to a single spermatozoon. Indeed, one might 

 infer from the evidence of the phenomena of fertilization that such must 

 be the case, and that the ingress of the spermatic element, in sexual forms, 

 is a consequence of the exhaustion of the power of continuous growth, as 

 shown in the abortive effort at spermatogenesis in the ^extrusion of the 

 polar bodies. A consequence, however, following because of the appe- 

 tency of the spermatozoon to set up a segmentation in the cytoplasm 

 which should end in a continuation of the process of spermatogenesis set 

 agoing by the expulsion of the polar bodies. Yet, this does not occur, 

 and, as -we have seen, a good reason can be assigned why spermatogenesis 

 does not go on indefinitely after being initiated by the extrusion of the 

 polar bodies. Equally good reasons can be assigned why the method of 

 nuclear movement is changed after the entrance of the spermatozoon. 

 On my view this is wholly due to the sudden advent of wholly new con- 

 ditions, since about the time of the ingress of the spermatozoon the egg is 

 not only cut off from its supply of nutriment and is now an isolated being 

 the whole of the cytoplasmic field of which is at the mercy of the com- 

 bined action of the pronuclei, while the preparatory equilibrium resulting 

 from the extrusion of the polar bodies has been attained beforehand. 



