m'clung: spermatocyte divisions of the looustid.k. 221 



"chromatin nucleolus' for the first time in the spermatocyte 

 generation." 



The noteworthy thing about this "chromosome x" is the fact 

 that in every essential detail it corresponds to the accessory 

 chromosome of the Orthoptera. It is a spermatogonial chro- 

 mosome that comes over intact into the spermatocyte ; it re- 

 tains its form and staining power unchanged through the 

 prophase of the spermatocyte ; it divides in only one of the 

 spermatocyte mitoses ; and is a large and conspicuous element 

 of the cell at all times. 



This "chromosome x" agrees just as closely in its descrip- 

 tion to the accessory chromosome as do the ordinary ones of 

 the two orders, and, if Montgomery's account is correct, there 

 would seem to be no reason for doubting their identity. In 

 two respects, however, there are differences between these 

 structures. First, it is to be noted that the "chromosome x' ; 

 divides in the first spermatocyte, while the accessory chromo- 

 some undergoes separation in the second spermatocyte. Should 

 Montgomery's observations prove correct, it would yet indicate 

 no fundamental difference in the character of the element, for 

 the result is the same whether division takes place in the first 

 or second mitosis. In either event, one-half the spermatozoa 

 are provided with the odd chromosome while the remaining 

 half are not. 



The second point of difference would seem to be a more seri- 

 ous one. Montgomery states that during the spermatogonial 

 mitosis the "chromosome x" regularly divides as do all the 

 other chromosomes, i. e., longitudinally. In the spermatocyte 

 mitosis, however, the element is broken across, and the longi- 

 tudinal split, which is apparent in the early stages, disappears 

 and is not utilized in division. We have here the remarkable 

 occurrence of a chromosome entirely unchanged in its structure, 

 but merely differing in its surroundings, which, instead of di- 

 viding along the plane marked out for it, as it has done in all 

 preceding mitoses, breaks across after it is a formed element. 

 An occurrence of this kind, so different from the usual method 

 of division, would require strong proof to establish it, and this, 

 in my opinion, Montgomery has not brought forward. 



A criticism of the degeneration theory as advocated by Paul- 

 mier and Montgomery has already been given (17), so that it 



