WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. 77 



figures 67 and 68) shows a more or less well-defined spiral condition. 

 This spiral is better shown in figure 69, where it is more unravelled. 

 Very soon after the process of uncoiling gives rise to the leptotene 

 threads, stages in conjugation may be seen. Figure 70 shows an early 

 leptotene stage with two threads which stain more deeply than the 

 others, having conjugated as far as they can be traced in this particular 

 section. I think we may identify these denser threads as the members 

 of the chromosome-pair A. 



The two sides of figure 70 are drawn differently. The left side is 

 diagrammatic and is intended to represent the apparent entanglement 

 of the leptotene threads. On the right side an attempt has been made 

 to follow individual threads. Careful study makes it evident that 

 the tlireads, instead of anastomosing, as they appear to do when one 

 makes only a superficial examination of them, are really continuous 

 and distinct for certain distances. The difficulty in following in- 

 dividual threads is due to the fact that after the early leptotene stage 

 the chromatin collects into chromomeres, which are strung along a 

 linin fiber, so fine and stainless in some places that it is scarcely trace- 

 able. When two such fibers cross each other in close proximity it is 

 sometimes almost impossible to trace the independent courses of the 

 two in the region of the apparent intersection. 



There is less difficulty, however, in tracing the threads of ^. At the 

 stage shown in figure 71 — which corresponds with that in figure 29 

 (Plate 3) the threads are very fine and well oriented. In this nucleus 

 there can be seen a loop of heavier threads (A), which have the ap- 

 pearance of being two, loosely wrapped around each other. The ac- 

 cessory, as shown at X, also forms a he^vy spireme loop at this stage, 

 but it is so much heavier than the one described that there can be no 

 confusion between the two. The deeply staining loop of interlaced 

 threads I interpret to be the spireme of the chromosome-pair A. In 

 figure 73 is shown an yl-spireme which has not completed its conjuga- 

 tion. It will be noticed that of the other threads in this nucleus 

 some are double and some are single; and, furthermore, that the 

 double ones are twice the width of the single ones. In figure 74 the 

 spiremes of the pair A have completely conjugated, though the general 

 appearance of the cell indicates that the stage is no further advanced 

 than that shown in figure 73. Figures 75-78 (Plate 7) show the pair 

 A in various stages of conjugation at stages closely corresponding to 

 those shown in figures 73 and 74. 



I have already traced the pair A from the pachytene stage to the 

 metaphase of the first spermatocyte division, so that it now remains to 



