180 FOOT-NOTES TO EVOLUTION. 
ing resting stage each spermatocyte now divided again, 
as in Fig. 11, # and F, each dyad now being separated 
into halves, so that in the spermatids of Fig. 11, #, but 
Fic. 11.—Reduction of chromosomes in the spermatogenesis of Ascaris 
megalocephala, var. bivalens; A, nucleus of a spermatogonium ; the 
typical number of chromosomes (four) is seen, each split longitu- 
dinally preparatory to the next division. B, young spindle stage of 
primary spermatocyte ; two tetrads are present, each formed by the 
double longitudinal splitting of a chromatin thread. C, the tetrads 
in the equatorial stage of the division. D, separation of dyads. 
E, the dyads in the succeeding division of the secondary spermato- 
cyte. F, completion of the division of the same ; each cell (sperma- 
tid) contains the reduced number of chromosomes (two). (After 
Brauer.) 
two chromatin masses are present. Thus the tetrads of 
the primary spermatocyte are divided up among the four 
spermatids, so that each of the latter receives one fourth 
