258 Edmund B. JVihon. 



velop from the various egg regions. This is quite in harmony 

 with Whitman's contention that "organization precedes cell-form- 

 ation and regulates it" {op. dt.^ p. 115). But, while in agree- 

 ment with the general spirit of his conclusions, as I understand 

 them, it seems to me that Whitman's statement does not sufficiently 

 recognize, first, the fact that the differentiating factors may un- 

 dergo so accurate and complete a distribution among the cells, 

 and be so largely emancipated from the general control as is 

 proved by my experiments — in other words, sufficient weight is 

 not given to the effects of precocious segregation; second, (and 

 here I should more distinctly take issue with him) that the cyto- 

 plasmic segregation or "organization" is a progressive or epigen- 

 etic process. 



As regards this second point, in my preceding paper I have en- 

 deavored to show that the Dentaliiim egg presents a form of pre- 

 cocious segregation (and localization) which in other forms, such 

 as the eggs of certain annelids, is acquired at a later period. The 

 facts observed by Boverl on the Strongylocentrotns egg, and the 

 experimental results of Yatsu, Zeleny and myself on Cerehratu- 

 lus clearly indicate that in these forms, too, the cytoplasmic seg- 

 regation is gradually effected, and at the time of the third cleav- 

 age has progressed further In the nemertine than in theechlnoderm. 

 There is, therefore, a legitimate basis for the conclusion that the 

 degree as well as the form of segregation existing at the begin- 

 ning of cleavage may vary more or less widely; and hence for the 

 further assumption that the mosaic character of the early cleav- 

 age stages may be expressed in different degrees. For this rea- 

 son, in so far as the term "organization" as used by Whitman is 

 applied to the cytoplasmic conditions, I am unable to accept his 

 conclusion that the eggs of different forms do not differ In degree 

 of "organization;" or that "Cell-orientation may enable us to 

 Infer organization, but to regard It as a measure of organization 

 Is a serious error" {op. cit., p. 109). Such a conclusion appears 

 to me a petitio principii in regard to the relation between the 

 nuclear and the cytoplasmic organizations, and that between "pre- 

 formed" and "epigenetic" qualities in the cytoplasm;^ and this 



^Cf. Boveri, 1902; Wilson, 1904. 



