324 ROBERT H. BOWEN. 



limit of their distribution being abrupt and constant. Thus the 

 mitochondria come to form a broad, equatorial girdle enclosing 

 the nucleus, and, as subsequent developments show, the spindle, 

 while the centrioles occupy the open ends of the sheath-like 

 girdle. Furthermore, the zone of cytoplasm around the cen- 

 trioles is delimited by the ends of threads, of which a few can 

 be seen in lateral view the main bulk of the threads being lost 

 in an equatorial tangle impossible of. analysis. The actual ar- 

 rangement in the vicinity of the centrioles is rendered much 

 clearer by a study of polar views or of sections cut obliquely 

 through one centriole. In direct polar views (Fig. 12), espe- 

 cially if the cell is somewhat flattened, the paired centrioles are 

 seen to occupy the center of a cytoplasmic area which in prepara- 

 tions properly fixed is seen to be the area toward which the astral 

 rays are converging. Around the edges of this clear area are 

 arranged the ends of the mitochondrial threads which radiate out 

 toward the equator of the cell like so many meridians of longi- 

 tude. In oblique sections through one polar area (Fig. 13), the 

 polarization of the threads toward the centrioles is very clear, 

 and in such views one can generally follow the individual threads 

 for some distance. It appears that the threads are quite variable 

 in length, some being relatively short while others are long, but 

 generally speaking any one thread seems to be oriented toward 

 a centriole at one end only, while the free end becomes more or 

 less bent and twisted and is lost in the tangle which encircles the 

 equator of the cell. In cross sections through the subequatorial 

 region, one sees for the most part only the ends of threads. It is 

 clear from the foregoing that the maze of threads in the sperma- 

 tocytes is untanglea during the prophases, apparently under the 

 influence of the centrioles, resulting finally in the polarization of 

 most (all?) of the threads toward the opposite centrioles, while 

 in the equatorial zone the free ends of the threads apparently 

 become lost in an inextricable tangle. 



Meanwhile the nuclear membrane fades out, the chromosomes 

 take up their position on the spindle and the metaphase figure of 

 the first maturation division is complete (Fig. 14). In sections 

 through the long axis of the spindle numerous threads can be 

 made out directed toward the centrioles, but in polar view the 

 orientation of the threads is usually less clear than in the pro- 



