﻿19031 BEHAVIOR OF THE CHHOMOSOMES 253 



minute detail, and I have nothing to add to my former account 

 of the process (JNIottier, '97), As soon as the chromatin spirem, 

 * which has split longitudinally, has segmented into the chromo- 



somes, each chromosome consists \n Lilium of two rather long 

 daughter segments. These segments may be variously oriented 

 toward each other even in the same nucleus. Sometimes they 

 may be separated entirely from each other, being connected 

 only by delicate threads; but, as is generally the case, they are 

 more or less closely applied and twisted upon each other 

 [Jig. /, a). Again, they may be attached to each other near the 

 middle or at one or both ends. In the latter case, the free ends 

 - may diverge variously {^fig. /, b, c). It frequently occurs that 

 the opposite ends adhere, while the middle portion bends out- 

 ward to form loops or rings {^fig. 2, b). In the majority of 

 mstances, it is clear that the daughter chromosomes are twisted 

 upon each other, and to this fact is due many of the peculiar 

 forms to be observed in the spindle stage. 



Between the time of the segmentation of the chromatin 

 spirem and the mature spindle, the chromosomes contract some- 

 what, becoming thereby shorter and thicker. They may lie 

 distributed along the nuclear membrane or irregularly scattered 

 t in the nuclear cavity. At this stage, however, w^e frequently 



} find the daughter segments so oriented toward each other as to 



present the various other forms often observed in the nuclear 



I 



w 



plate, such as loops, rings, X's, Y's, etc. With the development 

 of the spindle, which occurs in precisely the manner described 



Mott 



ally oriented in the nuclear plate {fig. s)- So far as can be 

 determined with .absolute certainty, each chromosome, up to the 

 stage of the mature spindle, is composed only of two daughter 

 segments, although in some cases a trace of the second longi- 

 tudmal fission may be seen in the seerments. It was this 



phenomenon that strengthened my former view that the chromo- 

 somes folded upon themselves during the development of the 

 spindle. 



As has been shown by numerous observers, the chromosomes 

 arranged in the nuclear plate present various forms and various 



'^v^t r 



