WENRICH: spermatogenesis of PHRYNOTETTIX MAGNUS. 6^ 



the plane of the primary split is never completed, but that the chroma- 

 tids again become separated at the proximal end, assuming the forms 

 shown at /to i, figure 62, and that the first division is therefore always 

 equational. However, the possibility of an occasional reductional 

 division as a result of the ring-formation must be taken into considera- 

 tion. 



2. Chromosome-pair B. Figure 63 (Plate 6) presents a series of 

 stages for B corresponding to those in figure 62 for A. This series of 

 stages of B supports the conclusions reached from a study of A in 

 regard to: — (1) a probable parallel, association in the pachytene 

 stages of pairs of threads, each representing individual chromosomes; 

 (2) the formation of the tetrad by, first, a separation along the plane 

 of conjugation (?". e., the primary longitudinal split) and, secondly, 

 by a splitting of each of the original conjugants (the secondary longi- 

 tudinal split) ; and (3), as a result, an equational division of the tetrada 

 at the first division. 



This chromosome-pair (B) is characterized by the presence of large 

 and well-marked polar granules at both ends and by a similar large 

 granule not far from the middle, though always somewhat nearer the 

 distal end. Leaving aside the formation of rings, the chief difference 

 in behavior between A and B is that jn the former the plane along 

 which the greatest separation takes place before metaphase is that of 

 the secondary longitudinal split, while in the latter the greatest separa- 

 tion takes place along the plane of the primary split. This results 

 in A becoming extended in the direction of the spindle-axis, as already 

 described, while B becomes extended at right angles to this axis. In 

 the latter case the separation along the plane of the primary split does 

 not become complete at the expense of the separation along the plane 

 of the secondary split, but the latter separation persists for a short 

 distance, giving rise to a cross with unequal arms (fig. 63, g, h). The 

 short arms terminate in the proximal or synaptic ends of the chroma- 

 tids, while the longer arms terminate in the distal ends. 



However, these differences in behavior between A and B are not 

 fundamental, since the final result, an equational division, is the same 

 in both cases. But they are indications of the individual peculiarities 

 of these elements. It should also be pointed out that such differences 

 could easily be misinterpreted, if only parts of the histories of the 

 pairs were known. 



It is important to note that the drawings of the series shown in 

 figure 63 were all taken from sections of a single testis. In searching- 

 for the same element in other individuals, I was surprised to find the 



