The Spermato genesis of Aplopus mayeri. 19 



mosomes == 36) which are occasionally met with, and these in turn to giant 

 spermatids and giant spermatozoa, which are also of frequent occurrence. 

 In the telophase of this mitosis a mid-body again appears, similar to that 

 of the previous division. At this stage the accessory chromosome is again 

 unrecognizable, having probably assumed a brief diffuse form, and is thus 

 lost among the ordinary chromosomes that are passing into the reticular 

 stage of the resting nucleus of the final order of secondary spermatogonia 

 (fig. 25). 



In the resting stage of the last order of secondary spermatogonia a 

 chromatin nucleolus (accessory chromosome) again appears in the almost 

 achromatic nuclear reticulum (fig. 26). Its contour is less sharp than in 

 the earlier spermatogonial stages, but it assumes its characteristic position 

 near or closely applied to the nuclear wall. In late stages of the prophase 

 it again appears bipartite. The chromatin again passes through the fine, 

 coarse, and segmented spireme stages (figs. 27, 28, 29, 30 and 31), and com- 

 pact chromosomes of comparatively small size and less variable form (35 in 

 number) are drawn into the equatorial plate (figs. 32 and 33). A pair of 

 chromosomes (daughter-chromosomes, products of a premature division) 

 are frequently observed to enter the spindle perpendicular to its fibers (figs. 

 34 and 35). This unique chromosome is probably the accessory, since the 

 latter had partially split already in the prophase. 



During metakinesis the dumb-bell-shaped chromosomes become more 

 and more elongate until at anaphase (fig. 36) the connecting chromatic 

 fiber is broken and the chromosomes pass into telophase again with one or 

 several pairs lagging behind (fig. 37). Late telophase stages are shown 

 in figures 38, 39, and 40, the latter as well as the subsequent stages again 

 showing a very conspicuous mid-body. Figures 41 and 42 show the chromo- 

 some complex at still later telophase, and the final stages succeed each other 

 in the order given in figures 43, 44, and 45. This time the accessory chromo- 

 some does not pass through a reticular stage as previously (or perhaps such a 

 phase is really assumed, but is of extreme brevity), for it is recognizable 

 as such among the granular pale-staining, indefinitely contoured chromo- 

 somes of the final stage of telophase. A brief resting stage now ensues, 

 during which the accessory chromosome is very conspicuous in the delicate 

 achromatic nuclear reticulum, of sharp contour and closely applied to the 

 nuclear wall (fig. 46). 



PRIMARY SPERMATOCYTE. 



The resting stage appears to be very transitory, for almost immediately 

 decided alterations begin to transpire in the nucleus. The reticulum gains 

 chromatin and occasional small karvosomes may appear (fig. 47). In the 

 next stage, which is of comparatively long duration, the reticulum has ar- 

 ranged itself into a close-meshed lattice-work of wide threads. The acces- 

 sory chromosome has an oval shape, intense staining capacity, and is closely 



