The Spermatogenesis of Aplopus mayeri. 17 
Karyokinesis is initiated by an increase of stainable material in the linin 
network, a subsequent diffusion of the karyosomes and the arrangement of 
the chromatin into a spireme. This segments into a number of coarse 
mossy or granular deep-staining threads, which give indication of a longi- 
tudinal split (fig. 5). Presently the split is consummated, and the seg- 
ments now assume the form of slender bipartite rods of varying length 
(fig. 6). By the time the chromosomes have entered the equatorial plate 
at the end of prophase, they have attained greater bulk, more definite con- 
tour, and greater affinity for basic dyes. The chomosomes are of various 
shapes, several are large and typically U-shaped, and the number is 35 
(figs. 7 and 8). During metakinesis (figs. 9 and 10) the chromosomes 
separate, probably along the line of the longitudinal split seen in the pro- 
phase, similar variations in size obtain as in the prophase, and the halves 
are drawn to their respective poles, thus producing two secondary sperma- 
togonia. Around these two cells a membrane appears—the persisting cell- 
wall of the mother primary spermatogonial cell—forming a two-celled sper- 
matocyst (fig. II). 
During metakinesis the only kinoplasmic structures which are clearly 
visible are the spindle fibers. In the late telophase a very conspicuous mid- 
body appears, composed of a row of minute, deep-staining granules. Figure 
13 shows a two-celled spermatocyst, one of the cells of which is in telophase. 
I have been able in my material to definitely determine upon at least three 
generations of secondary spermatogonia. There are probably several times 
as many, the early orders being so closely similar as to make identification 
uncertain. Sutton, in the case of Brachystola magna, was able to distin- 
guish seven or eight orders of secondary spermatogonia. There are also 
several—probably many—orders of primary spermatogonia in all essential 
respects identical. It is possible to distinguish the primary from the sec- 
ondary spermatogonia by the fact that the former have vesicular nuclei, 
often lobed, and a relatively small amount of chromatin, as well as by the 
fact that they are disposed irregularly and not in cysts, as are the older 
generations. From a telophase in which the daughter-chromosomes pass 
through a pale-staining granular stage arises the resting stage of the first 
order of the secondary spermatogonia. 
SECONDARY SPERMATOGONIUM. 
These cells in the various orders are in all respects similar until the 
final order is attained. It should be added here that the succession of events 
throughout the entire spermatogenesis could be definitely determined by the 
fact that cysts could always be found containing transition stages to and from 
the typical phase for that particular cyst, and these transition stages over- 
lapped in the several cysts to such an extent as to render clear the order 
of succession. In the resting stage of the first order of secondary spermato- 
