BIGELOW : NUCLEAR CYCLE OF GONIONEMUS MURBACHII. 325 



2.5 p in diameter, and its length in the metaphase only ahout 6 /*. As 

 far as the achromatic figure is concerned, it shows no marked differences 

 from those already described, except that the centrosome is larger (Fig. 

 85). This may be connected with the fact that it is fated to persist 

 throughout the entire course of division and in the daughter spermatid, 

 whereas in other cell generations it disappears in the telophase. The 

 spindle, as in all adult tissue cells of Gonionemus, wholly lacks astral 

 rays ; the spindle fibres are delicate, and rapidly dwindle during the 

 anaphase, but the interzonal filaments are stout, granular, deeply stain- 

 ing, and evidently entirely different in nature from the spindle fibres 

 (Fig. 86). 



In this, as in the first maturation division, there is but little internal 

 evidence to show whether it is to be regarded as reducing or equational. 

 The chromosomes in the present case divide rapidly (Fig. 85), never 

 formiiiLr the elongated dumb-bell-like structures so characteristic of the 

 former case (Fig. 64). Moreover, while it is impossible in the meta- 

 phase, to note any very decided diffei'ence between the size of the 

 chromosomes of the two maturation divisions, in the anaphase it is at 

 once apparent that in the second they are very much smaller than in 

 the first (compare Fig. 68 with Fig. 85). These conditions suggest 

 that we are dealing here with a reduction division. The evidence is, 

 however, too incomplete for any very definite conclusion as to the suc- 

 cession of the maturation divisions in Gonionemus. 



The later stages of division present no features of special interest. 

 During the anaphase the chromosomes of the two daughter plates are so 

 closely crowded that they appear to fuse (Fig. 86). But this is not 

 actually the case, for they soon move apart once more. They have now 

 lost their sharp contours and are connected, probably at their previous 

 points of contact, into an irregular network (Fig. S7). 



6. The Metamorphosis of the Spermatid. 



We may consider the stage shown in Figure 88 as the first in the his- 

 tory of the spermatid. Constriction of the cell body has taken place, 

 but the two daughter cells are still connected by a bridge of interzonal 

 filaments, at the middle point of which is a series of deeply stained in- 

 terzonal bodies. The most striking feature of this stage is the condition 

 of the centrosome. It will be recalled that in the case of the somatic 

 and spermatogonia! mitoses previously described, this body could not be 

 traced beyond the anaphase, and that it was always an exceedingly min- 

 ute granule. In the second maturation division, however, it is much 



