358 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ities indicate that it is composed of chromatin. The distinction 

 between this and the accessory is only possible when the ac- 

 cessory lies close to the nuclear membrane, which is its usual 

 position. In this respect it resembles the accessory chromo- 

 some of the first spermatocyte prophase of the Orthoptera. 



The history of the three distinct nuclear components, active 

 chromatin, accessory chromosome and plasmasome, will be fol- 

 lowed separately up to the spermatocyte metaphase, beginning 

 with the chromatin. The reorganization of the nuclear chro- 

 matin into typical spermatocyte chromosomes after diffusion is 

 completed gives no hint of a reversal of the mitotic cycle. 

 That is, the appearances which characterize chromosome re- 

 construction do not suggest a reversal of the changes which 

 were observed to take place in the diffusing chromatin. The 

 straight threads which typify the early prophase (figs. 1-4, 

 plate LX VI) gradually elongate and finally are disposed into a 

 fine reticulum at the intersections of which are very slight ac- 

 cumulations of chromatin. See figure 4, plate LXVI, and 

 figure 4, plate LXVII. This might be considered as the climax 

 of diffusion, for in this stage the chromatin is most evenly dis- 

 tributed throughout the nucleus. Subsequently there are more 

 extensive accumulations of chromatin at certain points within 

 the nucleus. These amorphous aggregations of granular 

 chromatin gradually assume the form of loosely organized 

 tetrads resembling a few of the types of tetrads found in the 

 Orthoptera. Figure 16, plate LXVI, shows four types of tet- 

 rads taken from one cyst all of the cells of which are in 

 the same stage of development; (a) shows the largest form. 

 By analysis it is seen to be composed of four equal chromatids 

 and represents the pair of the largest spermatogonial chromo- 

 somes conjugated. The disposition of maternal and paternal 

 chromatids is indeterminable in this as well as in the forms 

 shown by (b) and (c), which are different types of the cross. 

 In each case two opposite arms of the cross are composed of 

 portions of maternal and paternal threads lying parallel to 

 each other. The ends of these arms are the synaptic ends of 

 the chromatids, but whether the synaptic end of a chromatid 

 represents the polar end, as is certainly the case in the 

 Orthoptera,* it is impossible to determine. One of the other 

 pair of opposite arms is composed of parallel maternal threads 

 and the remaining arm consists of parallel paternal threads ; 



* Pinney, Edith, OrKanization of the Chromosomes in Phrynotettix magnus, Kansas 

 University Science Bulletin, vol. IV, No. 14, 1908. 



