124 LOUISE B. WALLACE. 



mately accurate count of them (Figs, i and 2). It was also not 

 found possible to identify at this stage the accessory chromosomes 

 among the other rod-shaped chromosomes. The centrosomes 

 are quite distinct and the spindle fibers have a tendency to bulge 

 out, forming a spindle with convex sides. This is probably owing 

 to the large size of the chromosomes and to the large number 

 of fibers which must be accommodated between the centrosomes 

 and the equatorial plate. In division the rods split longitudinally 

 and the resultant halves move toward the opposite poles. In 

 anaphase two pairs of daughter chromosomes appear distinct from 

 the others both on account of their large size and because they 

 are slower in passing to the poles (Figs. 3 and 4). While this 

 might well be looked upon as simply a case of retarded division, 

 in the light of what follows it seems probable that they are the 

 accessory chromosomes which have the form of a pair of rods 

 throughout the greater part of their subsequent history. In 

 telophase the ordinary chromosomes gradually become granular 

 but their identity is still traceable in the loose, irregular masses 

 scattered through the nuclear cavity. These masses stain but 

 faintly, and in iron-haematoxylin preparations, when the extrac- 

 tion of the dye has not been carried further than usual, they are 

 nearly colorless. The accessory chromosomes, on the other 

 hand, retain the rod-like form and lie near the periphery of the 

 nucleus. 



Spermatocytes. 



In Fig. 5 is shown the early prophase of the primary sperma- 

 tocyte in which the chromatin masses are becoming looser, more 

 granular, until finally the processes of adjacent ones meet on the 

 threads of the linin reticulum. The nucleus swells with the 

 accumulation of nuclear sap and at the same time the cytoplasm 

 is reduced to a rather thin layer around the swollen nucleus. 

 The accessory chromosomes lose their rod-like form and appear 

 as two densely staining, chromatin nucleoli often lying at some 

 distance apart (Fig. 6). Later these two chromatin nucleoli 

 approach one another and finally unite to form a single, large, 

 irregular mass which is a conspicuous body in the resting stage 

 (Fig. 7). This is followed by the contraction stage when the 

 whole cell is noticeably reduced in size and the nuclear contents. 



