WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. 67 



Stage Total Expanded Not expanded % Expanded 



Spireme HI 94 7 93.06 



Postspireme 162 146 16 90.12 



Both stages 273 240 23 91.26 



"f^ 



It will be seen from this table that approximately 90% (examples 

 counted at random) have one of the granules in the expanded condi- 

 tion. In the postspireme stages this peculiarity appears less like an 

 expanded single granule than as a group of closely associated small 

 granules, typically three in number. This condition will be discussed 

 more fully in another place (p. 112). In both the spireme and the 

 postspireme stages the modified polar granule furnishes a ready means 

 of identification of chromosome-pair A, especially when its staining 

 qualities, already described, are taken into consideration. The con- 

 stant relative size of A in the tetrad stages is also a help in identifica- 

 tion. 



Figure 62 (Plate 6) indicates clearly the processes by which the 

 spireme loop becomes first transformed into a typical tetrad, and then 

 condensed to a metaphase chromosome. From the zygotene stage 

 onward, there is a gradual shortening of the spireme loops or segments. 

 The later stages of this process are to be seen in figure 62. Through- 

 out the pachytene stage the spireme loops exhibit a median longi- 

 tudinal cleft, usually referred to as the longitudinal split. I shall call 

 this the primary longitudinal split. Occasionally paired granules, or 

 chromomeres, appear to be fused together, but as a general rule, the 

 split is continuous throughout the length of the loop. In my opinion 

 this so-called longitudinal split is really the space between two spireme 

 (leptotene) threads which have conjugated side-by-side. Fm-ther evi- 

 dence for this belief will be presented later. 



Figure 62, c, indicates the first step in the process of forming the 

 four chromatids of the tetrad. A second longitudinal split, at right 

 angles to the first or primary split, begins at the proximal end (upper 

 end in the figures) of the free spireme segment (fig. 62, c) and gradually 

 proceeds toward the distal (lower) end (fig. 62, c-c). It will be seen 

 from these figures that as the separation produced by the secondary 

 split proceeds distally, the separated chromatids at the same time 

 reunite along the plane of the primary split. The separation due to 

 the secondary split gradually increases until the diverging pairs of 

 chromatids extend in opposite directions, thus forming a rod-like 

 element the two ends of which correspond to the proximal pole of the 



