The Spermato genesis of Aplopus inayeri. 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. n). 



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. Button, in the case of Brachystola magnet, 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 SPERM ATOGONIUM. 



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-- 



