M'CLUNG : SPERMATOCYTE DIVISIONS OF THE LOCUSTID.K. 193 



participates normally in the mitoses of the secondary sperma- 

 togonia. Tt is here distinctly visible because of its large size, 

 which causes it to extend down to the equatorial plate, while 

 the other chromosomes are in a late anaphase. 



At the close of the spermatogonial divisions, when the dis- 

 ruptive processes reduce the other chromosomes to masses of 

 chromomeres in which chromosome identities are not apparent, 

 the accessory chromosome, with apparently more cohesive vigor 

 than the others, retains its general form and is at all times dis- 

 tinguishable. It is marked off from the others, not only by 

 persistence of form, but also by the difference in staining reac- 

 tion, this being such as is usually exhibited by chromatin when 

 concentrated into homogeneous masses. While studying the 

 cells of Xiphidium, I noticed that, at one stage, this color re- 

 action changed somewhat and more nearly approached that of 

 the diffused chromatin. At this time the accessory chromo- 

 some had the form of a flattened, apparently fenestrated, plate. 

 I have been fortunate enough, in preparations of Orchesticus, to 

 discover that the accessory is really at this time in the form of 

 a long, coiled thread (fig. 5) . It is thus seen that, even in re- 

 spect to the spireme stage, the accessory chromosome is com- 

 parable to the others, the only difference being that the diffusion 

 of the chromomeres is less, and the independence of the element 

 greater, than is the case with the other chromosomes. 



As the chromatin segments shorten and thicken, the thread 

 of the accessory likewise increases in diameter at the expense 

 of its length, and is finally observable in various degrees of 

 contortion, as shown in figure 12. By the time the chromo- 

 somes are ready for division, the accessory has assumed a form 

 very similar to that it shows in the spermatogonia. With the 

 establishment of the equatorial plate, the accessory moves to one 

 pole of the spindle and there remains undivided during the first 

 spermatocyte mitosis. It is accordingly a member of only one 

 second spermatocyte resulting from the division of each first 

 spermatocyte. 



Returning to the group of chromosomes preparing for meta- 

 kinesis, we find that in their earlier stages they lie so that their 

 longer diameter is in the equatorial plate, while attached to the 

 enlargement in the center of each, representing the point of 

 separation laid out for the second spermatocyte division, are 



