M CLUNG : SPERMATOCYTE DIVISIONS OF THE ACRIDID.E. 81 



In the stages represented in Figs. 15, loa and IT are liroiight out 

 several points which I wish to emphasize. It will be noted in several 

 of the elements that the lines of the two divisions are very clearly 

 marked, particularly so in the one represented in Fig. 17. It will 

 also be observed, in this element, that the chromatids have moved 

 upon each other along the line of the cross-division to such an extent 

 that the arms of the resulting cross-figure approximate each other in 

 length. This movement is a very significant one, as I hope to show 

 in considering the later stages of division. 



The lines of separation between the chromatids, so i^lainly appar- 

 ent in these early stages, entirely disappear with the subsequent con- 

 centration of the chromatin elements, and it is only the general 

 outline of the chromosome and a knowledge of its formation that 

 enables us to understand what takes place during division. 



A great change in the constitution of the chromosomes occurs as 

 the metaphase of the first spermatocyte division is approached. 

 During the early prophases, the rings, loops and rods occurring in 

 the nucleus all display the diffused granular condition represented in 

 the figures. The essential feature of their further develoj^ment con- 

 sists in the concentration of the chromatic material. As a result of 

 this, the elements become smaller and denser and all lines of division 

 between the chromomeres become indistinguishable. This is true 

 not only of those in the same chromatid, but of those between chro- 

 matids, so that the chromosomes in the nuclear plate appear to be 

 simple homogeneous bodies. 



From what follows in the resulting early anaphases, it would ap- 

 l^ear that the chromatids of each chromosome are bound together by 

 certain intrinsic forces which maintain a unit element so long as they 

 are undisturbed. The result is an obliteration, but not destruction, 

 of the individuality of the constituent elements. This is very i^lainly 

 apparent in their later behavior. Thus, immediately after the halves 

 of the chromosomes are separated in the metaphase, the free ends, not 

 attached to the spindle fibers, immediately diverge, showing a line of 

 separation between the two chromatids, which is quite indistinguish- 

 able in the apparently simple rod which they constituted. 



This coalescence of the elements and their ability to move along 

 each other, as shown in the earlier prophases, put us in possession 

 of the necessary facts to determine the exact character of the sperma- 

 tocyte divisions. 



I now wish to call attention to Figs. 18, 19, and 20, which exhibit 

 the metaphase of the first spermatocyte division. The great variation 

 in the form of the chromosomes was for some time very puzzling, 

 and it was not until I had made out their constitution that I could 



6— K.U.Qr. A— ix 1 



