534 Edmund B. Wilson. 



instances in regard to the spermatogonial number (e. g., in 

 Euschistus variolarius, Nezara and Brochymena). The state- 

 ment given in the general summing up of his latest paper ('05) 

 "Whenever the heterochromosomes occur in pairs in the sper- 

 matogonia they (/. e., the 'chromatin nucleoli') always conjugate 

 to form bivalent ones in the first spermatocytes, and their univalent 

 components become separated in the first maturation mitosis, /. e., 

 divide prereductionally" (p. 195, and elsewhere), is inapplicable 

 to the idiochromosomes; for even though they conjugate to form 

 a bivalent chromosome-nucleolus in the growth-period they again, 

 separate to divide as separate univalents in the first mitosis, as I 

 showed in detail in Brochymena, and as must also occur in the 

 other forms (as is proved by the number of the chromosomes and 

 their later history). The statement cited above applies only to 

 the w-chromosomes of such forms as Anasa, Chariesterus, Alydus, 

 Archimerus or Protenor; but the name "chromatin nucleoli" is 

 in these cases not very appropriate in view of the fact that in the 

 very form (Anasa) in which they were first discovered they do not 

 appear as chromatin-nucleoli at any time during the growth- 

 period of the spermatocytes. As to their behavior in the rest- 

 period of the spermatogonia I have at present no opinion to-express. 

 It is further probable that the distinction urged by Montgomery 

 between the "odd chromosome" and the accessory ('05, p. 192) 

 is also not valid; for my observations prove that in Alydus and 

 Archimerus the "odd chromosome" ("accessory") is a typical 

 chromosome-nucleolus (i. e., "heterochromosome") in the growth- 

 period, and it is extremely probable that the same will be 

 found to hold true of the "odd chromosome" of Harmostes and 

 QEdancala. I think therefore that Montgomery's general con- 

 clusions regarding the "heterochromosomes" require some 

 revision. 



We may now briefly consider the nature of the "accessory" or 

 heterotropic chromosome. So long as any of the forms possessing 

 such a chromosome were supposed to have an even number 

 of spermatogonial chromosomes the conclusion drawn by Mont- 

 gomery ('01, '04, '05) that this chromosome is a bivalent seemed 

 an almost necessary one, even in cases where it appears as a 

 single body in the spermatogonia. The observations brought 

 forward in this paper cast grave doubt, I think, on all of the 

 earlier accounts asserting an even spermatogonial number in 



