82 KANSAS UNIVERSITY QUARTERLY. 



understand the meaning of this diversity of form. Once understood, 

 however, the process is one of extreme simplicity. In Fig. 22 I have 

 drawn a number of chromosomes under the camera lucida which show 

 the progressive changes undergone by them during division. Those 

 from a to e lay in the equatorial plate of one nucleus, and are as clear 

 as diagrams in their indication of the intrachromosomal movements. 



At a, the chromosome lies with its longer diameter (corresponding 

 to the length of the thread from which it is derived ) in the equatorial 

 plane. At its center (which represents the point where the cross- 

 division is indicated in the earlier prophases) are attached the fibers of 

 the spindle. At b is shown an early effect of the fiber contraction, 

 which results in the formation of a cross-figure with its longer arm in 

 the equatorial plate (comjoare this with the chromatin element shown 

 in Fig. 17). A further contraction of the fibers brings about a length- 

 ening of the arms to which they are attached, and a corresponding short- 

 ening of those lying across their axis. This continues until the result 

 indicated at d is reached. It will be noted that this chromosome has 

 almost exactly the same form as that of a, except that its longer diam- 

 eter lies parallel to the axis of the spindle. The traction exerted by 

 the fibers continues until the halves of the chromosome are separated, 

 as shown in e,f, and g. At h is presented a chromosome of the stage 

 represented at a, but viewed from the pole of the cell. Imagine 

 the ends of the structure to be brought around until they coalesce, 

 when the ring represented at i will be formed. 



Knowing the composition of the chromosome, one can easily con- 

 ceive what takes place during the separation of its halves. It is evi- 

 dent that the chromatids on each side of the longitudinal division, 

 acted upon by the contracting fibers, move along upon each other 

 as they did during the earlier prophase when their structure was 

 less dense and the spaces between them were manifest. That the 

 demarkation between the chromatids was not lost is evident from 

 an examination of Fig. 21. Here it is observable that the diads, 

 shortly after they have separated, exhibit their dual nature by spring- 

 ing apart at the ends not attached to the fibers. This plane of sepa- 

 ration doubtless existed in the tetrad, but on account of the cohesive 

 forces prevailing in the element it was not visible. Immediately 

 upon the destruction of the balance of forces there established, how- 

 ever, the elements separated and manifested their individuality. 



There is no question, I think, but what the division of the chomo- 

 somes in the first spermatocyte of Hippiscus takes place as I have 

 indicated, and an examination of many other Orthopteran species 

 leads me to believe that it is the usual method of division in this 

 order. Indeed, I should not be surprised if it were a method com- 



