Studies on Chromosomes. 511 



(Cf. Paulmier's Figs. 28, 34-36, and my Fig. 2, k-n.) Both in 

 Anasa and in Alydus careful search among longitudinal sections 

 of the second division shows in fact in the clearest manner, that 

 the "small dyad" divides into equal halves, so that each of the 

 spermatids received one of its products (Figs. I, i-m\ 2, m, n). 

 The heterotropic chromosome is a much larger body, as shown 

 by the figures, in Anasa fully equal in size to some of the larger 

 single chromosomes of the anaphases of the second division. 

 Paulmier's failure to observe the second division of the small 

 bivalent is easily explained by the difficulty of observing this body 

 owing to its usually central or subcentral position, and the mistake 

 was a very natural one at the time his paper was written. Had he 

 examined Alydus where there are but seven chromosomes, which 

 show marked and constant size-differences, he could not have 

 failed to observe this division. 



We have now to examine a second and more difficult point, 

 namely, the nature of the condensed nucleolus-like body 

 (chromosome-nucleolus) of the growth-period, which so closely 

 simulates the heterotropic chromosome of the Orthoptera at the 

 corresponding period. I have always doubted Paulmier's and 

 Montgomery's conclusion that this body is the microchromosome- 

 bivalent, from the fact, clearly shown in the figures of both these 

 authors, that the chromosome-nucleolus of the synaptic and 

 growth-periods is always larger, and in some species very much 

 larger (e. g., in Alydus) 1 than the two spermatogonial micro- 

 chromosomes taken together, or than the small central bivalent 

 to which it was assumed to give rise. (Cf. Paulmier's Figs. 16-21, 

 with 26, 28.) This fact did not escape Montgomery's attention, 

 but he explained it as due to an increase of volume on the part 

 of the chromatin-nucleolus in the early growth-period and a 

 corresponding decrease in the late growth-period or in the pro- 

 phases of the first division ('01, p. 203). This explanation was, 

 however, not supported by any sufficient evidence; 2 and the only 

 detailed evidence on this point has been brought forward by 

 Gross ('04) in the case of Syromastes. This observer, however, 

 while apparently confirming Paulmier and Montgomery as to 



l Cf. Montgomery, '01, Figs. 96-98. 



^Montgomery's study of the facts in Euschistus ('98) is not in point, since he was here undoubtedly 

 dealing with the idiochromosomes and not with the w-chromosomes. 



