1909.] 



Gametogeiiesis of the Gall- Fly, etc. 



93 



Copeland in the corresponding stage in the Bee.* Fine threads run down 

 from this to the nucleus, but it is difficult to determine whether they 

 penetrate inside the membrane or pass outside it, for at the narrow end 

 the nuclear membrane becomes indistinct and confused with these fibres, 

 while remaining clearly defined at the opposite wider pole. 



The stage now described resembles the metaphase of a true division, such 

 as occurs later, but is distinguished from it by the ]iersistent nuclear 

 membrane, and the position of the chromosomes at one end of tlie nucleus, 

 near the broad end of the cell. In this case no nuclear division takes ])lace, 

 the nucleus becomes oval in shape, and the chromosomes generally contract 

 to form a compact mass lying across its centre (figs. 7 b, 8). In some cells 

 at least this chromatin mass seems to divide, half passing to each end of the 

 oval nucleus, and as this returns to its resting condition it is common to 

 find a cap of chromatic material at each pole. The chromatin may finally 

 disperse, taking the form of granules, and thus giving rise to a condition not 

 differing greatly in appearance from the primary spermatocyte in which the 

 chromatin has begun to appear. Possibly the division of the chromatin 

 inside the nucleus, which occasionally seems to occur, is the persistent 

 remnant of a true nuclear division, or it may perhaps be compared with the 

 " intranuclear karyokinesis " described by Kostaneckij in parthenogenetic eggs 

 of Mactra. 



While the nucleus is returning to its resting condition, the apex of the 

 pointed end of the cell, with the centrosome, becomes constricted off, 

 apparently much in the same way as in the Bee. The amount of cytoplasm 

 removed with the centrosome is very small, but it may sometimes be seen 

 attached to the body of the cell by a narrow bridge containing spindle- 

 fibres (fig. 7 h). In some cases the separation seems to be complete, and in 

 follicles containing spermatocytes with a reconstituted nucleus small loose 

 pieces of cytoplasm, sometimes witl: the centrosome visible at one end, are 

 found scattered among the cells. In other cases these fragments seem tO' 

 remain attached to the cell, but soon degenerate ; in the prophase of the-' 

 succeeding division they are perhaps represented by small knob-like 

 excrescences sometimes found at the edge of the cell (figs. 8, 9, 10 c). 



The cells with reconstituted nuclei may now be regarded as secondary 

 spermatocytes, although no true nuclear division has occurred. In their 

 resting condition, the duration of which it is not easy to determine, 

 they do not differ greatly from the primary spermatocytes when the 

 chromatin is beginning to appear; but they are generally more elongated, 



* ' Proc. Amer. Acad. Arts and Sciences,' vol. 42, No. 5, fig. 8. 

 t ' Ai-ch. Mikr. Anat.,' vol. 64, 1904, p. 1. 

 VOL. LXXXII. — B. I 



