290 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ZOOLOGICAL LABORATOEX. 



not an irregular V. If viewed from the pole it would easily 

 be seen to be a ring. The ends or tags pulled out, and to which 

 the spindle fibers are attached, are evidently what he de- 

 scribes as "ends of the univalent halves of the tetrad pulled 

 past each other." In other words, he considers the ring chro- 

 mosome a loop and these points where the fibers attach, these 

 projections that stick out on opposite sides, the crossed ends 

 of the loop gliding past each other. He believes that one uni- 

 valent half of the bivalent ring is simply being pulled away 

 from the other half, one spermatogonial member from the 

 other. But I am sure that he is entirely mistaken in this. 

 These tags or projections are the ends (XX of the figures) 

 of the transverse axis of the cross (a cross here modified to a 

 ring) . He has not taken into account at all the prophase form 

 of the ring (fig. 29), which shows beyond a doubt the origin 

 of these tags or projections. There it may be seen that each 

 projection is made up of part of one univalent half and of part 

 of the other univalent half of the ring. The ring may be 

 thought of as a split ring, and the split halves of it as being 

 pulled apart or as starting to move apart in the region (XX) 

 where the projections arise, one half going to one pole and 

 the other half to the other pole. This is the explanation that 

 the prophase form of the ring affords, and it would be absurd 

 to argue that the metaphase rings are anything more or less 

 than prophase rings that have become very much condensed. 

 Some of the chromosomes, possibly the smaller ones, may di- 

 vide transversely, but no evidence has been found to confirm 

 this view. I feel quite sure, therefore, that chromosomes 

 of the ring and cross type do not divide transversely but longi- 

 tudinally in this first maturation mitosis. 



The last and most important correction which I have to 

 make is in regard to the history of the accessory or "hetero- 

 chromosome." Montgomery describes it as a bivalent element, 

 not univalent, as it has up to this time been described for the 

 Acrididse and for Orthoptera in general. His mistake is due, 

 in part at least, to some large chromatin-like nucleolar struc- 

 tures that are present, at first as two bodies and later as one, 

 in the resting period between the last spermatogonial and the 

 first spermatocyte division. He finds the accessory in the 

 spermatogonia appearing for the first time in the form of a 

 single coiled spireme enclosed within a vesicle of its own, some- 



