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define fecundation as a more or less complete approximation of 

 two projiuclei, just so soon as they can be cotisidered a single mor- 

 phological element in the ovtmi. 



The facts which seemed to support this view I have already- 

 presented elsewhere.! j have since determined, in the newt 

 {Diemyctyhis viridescens, Raf.), through the kindness of my 

 friend, Dr. Edwin O. Jordan, that the two sexual cells which 

 react differently in an unmistakable manner, to the micro- 

 chemical test during the whole stage of their maturation, and 

 during the early stages of fecundation, become more and more 

 alike toward the completion of the latter process, and at the 

 time when the two pronuclei come closely into contact, the 

 micro-chemical reactions of the "male" and the "female" 

 pronuclei become identical. Similar results were obtained by 

 Lukjanow, as has already been mentioned, in the Ascaris of the 

 dog. Lukjanow killed the ovum with corrosive sublimate, and 

 applied the differential method of staining to the pronuclei. 

 Lukjanow's staining substance consisted of haematoxylin, saf- 

 ranin, and aurantia. The micro-chemical reactions of the two 

 pronuclei, according to this method, are "almost completely 

 alike," although there exist some slight differences as in the 

 number of vacuoles in the nucleolus and in other minor points. 

 My study on the same subject leads essentially to the same 

 result as that of Lukjanow, although pursued with different 

 methods and on a different animal. The difference which exists 

 between the two pronuclei is simply the difference which distin- 

 guishes one individual from another of the same species, as was 

 pointed out by Weismann. 



(4) I have already mentioned elsewhere that the sperm-cell 

 undergoes a much more varied series of changes of form and 

 of color-reaction during the period of its maturation than does 

 the ovum in the corresponding period. Thus the law of the 

 greater complexity of the male type of development as compared 

 with that of the female type in " secondary sexual characters," 

 as recognized by Hunter and Darwin, extends even to the 

 essential parts of the "primary sexual character." In short, 

 the phenomena of sex-differentiation extend through the whole 

 organization, including both the "germinal " and the " personal" 



1 On the Significance of Spermatogenesis (Abstract), Amer. Nat., July, 1892. 



