1^4 Edmund B. Wilson 



brought forward in this critique reply has already been made by 

 Boveri ('07), Strasburger ('08), Schreiner ('08) Bonnevie ('08) and 

 others. Some of the difficulties are real, but an attentive study 

 of the matter will show that a large part of Pick's critique is 

 directed against the strict hypothesis of individuality and offers no 

 adequate interpretation of the essential phenomenon that requires 

 explanation. It may be admitted that many of the facts seem at 

 present difficult to reconcile with the view that the identity of the 

 chromosomes as actual individuals is maintained in the "resting" 

 nucleus; and I have myself indicated (The Cell, 1900, p. 300) that 

 the name "individuality" was perhaps not the best that could have 

 been chosen. Certainly we have as yet comparatively little evi- 

 dence that the chromosomes retain their boundaries in the "rest- 

 ing" nucleus. It is evident that the chromosomes are greatly 

 diffused in the nuclear network, and it may be that the substances 

 of different chromosomes are more or less intermingled at this time. 

 Pick's "manoeuvre-hypothesis," which treats the chromosomes 

 of the dividing cell as temporary "tactic formations," may there- 

 fore be in some respects a more correct formulation of the facts 

 than that given by the hypothesis of "individuality" in the strict 

 sense of the term. But the last word on this question has by no 

 means yet been spoken. A new light is thrown on it by the recent 

 important work of Bonnevie ('08) which brings forward strong 

 evidence to show that in rapidly dividing cells (cleavage stages 

 of Ascaris, root-tips of Allium), although the identity of the orig- 



(both here and in the later passage at p. 98) will wholly mislead a reader not familiar with Moenkhaus' 

 work, in regard to one of the most significant and important discoveries in this whole field of inquiry. 

 Hardly less misleading is Professor Pick's report of my own observations on the sex-chromosomes 

 of insects, which are stated as follows: "Wilson's Unterschungen beweisen eben sicker nur soviel, dass 

 bei einigen Insektengattungen constante Beziehungen zwischen dem Geschlecht und dem Vorhandensein 

 eines besonderen Chromosomenpaares bestehen, bei anderen Gattungen nicht'" (p. 90). I am confident 

 that those who are familiar with the researches referred to will not accept this as a fair statement of the 

 results. The fact is that in one form or other the sex-chromosomes are present in all of the forms that 

 I have examined (now upwards of seventy species) and that with various modifications all conform to the 

 same fundamental type. It is true that in two genera (Nezara and Oncopeltus) the sex-chromosomes 

 are equal in size, and hence afford no visible differential between the somatic groups of the two sexes; 

 but I especially emphasized the fact (cf. '06, pp. 17, 34) that these chromosomes are in every other 

 respect identical with those of other forms in which the size-difference clearly appears, and are connected 

 with the latter by a series of intermediate gradations that leaves no doubt of the essential uniformity of 

 the phenomena. 



