62 THOS. H. MONTGOMERY jr., 



d) The 2nd sperm atocy tic division. 



As far as I could determine, the centrosomes remain single during 

 this division, though they are now so small that this point could not 

 be satisfactorily settled (Figs. 201—206, 213-219). 



This division takes place at right angles to the former one, 

 following the position of the centrosomes. But since the 1st spermato- 

 cytic spindle lies in no regular position with regard to the axis of the 

 testicle, the position of the axis of a spindle is no criterion of the 

 stage of division ; in Pprrhocoris (Uenking), on the contrary, the spindle 

 does occupy a fixed position at a given generation. The centrosomes 

 always lie close to the cell membrane, and are often in actual contact 

 with it. The 7 chromosomes and the chromatin nucleolus gradually 

 become arranged in the equator of the spindle (Figs. 203 — 205, 213 

 — 216), their axes parallel to the latter, and the plane of their con- 

 strictions perpendicular to it. Then follows the metakinesis (Figs. 217 

 — 219), with a consequent transverse (reduction) division of all the 

 chromosomes, and apparently in most cases of the chromatin nucleolus, 

 with the result that each daughter cell (spermatid) receives 7 daughter 

 chromosomes and 1 daughter nucleolus. Thus this division is like 

 the preceding. In the dyaster stage, when the spindle has become 

 noticeably elongated, the chromosomes of each spermatid fuse together 

 and so form a dense mass of chromatin, usually in the form of a 

 thickened disc placed perpendicularly to the spindle axis (Figs. 221 

 — 224); this disc has the same volume in cells of the large and small 

 generations, though the spermatids of the former are nearly double 

 the size of those of the latter. The pole rays and mantle fibres now 

 disappear, and the cytoplasm commences to arrange itself into the 

 state characteristic for the resting cell. The connective fibres, en- 

 veloped by a sheath of idiozome substance (Id.Z), persist still for a 

 considerable time. The cell body has constricted as far as the bundle 

 of these fibres (Figs. 218, 219). When the constriction has gone so 

 far, there appears a thickened granule at the equator of each fibre, 

 so that on longitudinal section of the dyaster these thickenings, being 

 situated close together, present the appearance of a beaded line 

 (Fig. 224); but they do not form a continuous plate. Lastly the 

 spermatids separate in the equator of the connective fibres also 

 (Fig. 222), but whether the line of separation bisects the granules of 

 these fibres could not be determined. The latter appear to be merely 

 thickenings of the fibres of the central spindle or of the connective 



