294 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATORY. 



the other chromosomes indicates, and is now on its way to the 

 lower spindle pole. That this is the case is shown also by the 

 spindle fibers, for they are evidently exerting an influence 

 on the ordinary chromosomes, since the latter are in the act of 

 dividing. The accessory, as his own drawing shows, is at- 

 tached by these fibers to but one of the poles, and that fiber 

 must evidently be pulling it toward its pole. This is a point 

 in which acuticornis agrees entirely with admirabilis (figs. 

 34, 35, 36). But chromosome Y of his figures 32 and 34 is 

 positively not the accessory, because that element, we have 

 found, does not divide in the first maturation mitosis but passes 

 over undivided (figs. 37, 38 and 39) to one of the daughter- 

 cells or second spermatocytes. He was therefore wrong in 

 identifying it with the Y of his figure 33. If he had examined 

 the full number of chromosomes in these cells (his figs. 32 and 

 34) he would undoubtedly have found the accessory in its 

 peculiar position starting off ahead of its fellows, as he found 

 it in figure 33. 



The heterochromosome of Syrbula is therefore not a bivalent 

 structure, for it is paired at no time during its whole course. 

 It does not divide in the first maturation mitosis but in the 

 second. Montgomery quotes McClung as describing "for Hip- 

 piscus an accessory chromosome of the spermatocyte, said to 

 divide in both maturation mitoses." This is a mistake. Mc- 

 Clung gives no such description. As he was unable at the 

 time to follow it farther or to distinguish it from the ordinary 

 chromosomes after it had taken up its position in the meta- 

 phase of the first division he merely supposed that it must 

 behave like the other chromosomes, and with that remark left 

 it, expressing the intention of making it the subject of a sub- 

 sequent paper. Since that time it has been found to behave 

 as in other Orthoptera, dividing only in the second division. 



And now Montgomery attempts to reconcile the "double 

 heterochromosomes" of the Hemiptera with the single hetero- 

 chromosome or accessory of the Orthoptera. His suggestion 

 is as follows : "In the Orthoptera the heterochromosome is 

 single in the spermatogonia; single therefore in the sperma- 

 tocytes, it does not divide in the first maturation mitosis, but 

 does in the second. Because it does not divide in the first 

 mitosis it must be either univalent or else, already in the sper- 

 matogonia, be composed of two so firmly united that they can- 



