spermatogenesis 499 



cepa than like the other two species of Poeciloptera. P. septen- 

 trionahs and P. pruinosa were found on the nettle and the other 

 two species came from sweepmg low grasses. In this material, 

 the cells and chromosomes are large and the achromatic struc- 

 tures especially well preserved. The material fixed in Flemming, 

 and stained in thionin makes some of the clearest preparations 

 included in this study. 



Poeciloptera septentrionalis 



The resting spermatogonia of this form are small and stain 

 lightly (Fig. 256). In preparation for division, a spireme is 

 formed, each granule of which splits longitudinally (Fig. 257). 

 The chromatic part of the spireme segments, retaining the linin 

 connections and also an indication of the longitudinal split (Fig. 

 258). There are 27 chromosomes in the spermatogonial plate, 

 two longer than the others {a^ and a., of Fig. 259). Fig. 260 shows 

 distinctly that this division follows the preliminary longitudinal 

 split. After the telophase, the chromosomes become more diffuse 

 and join into a spireme (Fig. 262). This spireme contracts into a 

 small dense ball at one side of the nucleus (Fig. 263), and then the 

 cell goes through a long growth period in which the diameter is at 

 least doubled. The odd chromosome appears as soon as the 

 spireme becomes pale enough to conceal it no longer (Fig. 264). 

 Then a pair of 777-chromosomes appears and a small plasmosome 

 (Fig. 265). The plasmosome and odd chromosome both increase 

 in size, the latter having a vacuole in the center (Fig. 266). The 

 odd chromosome has now attained its full size, but while the cell 

 and nucleus continue to increase, the plasmosome keeps on grow- 

 ing (Fig. 267). Even though it is now larger than the odd chromo- 

 some, it stains scarcely at all, while the odd chromosome and the 

 wz-chromosomes stain a deep blue, thus demonstrating the valu- 

 able differentiating powers of thionin. In the next stage (Fig. 268) 

 the odd chromosome and the plasmosome are unchanged, but the 

 spireme stains more deeply and shows a longitudinal split. The m- 

 chromosomes no longer appear, they have probably become indis- 

 tinguishable from the other spireme segments. The plasmosome 

 and odd chromosome still keep the same relative size in the pro- 



