No. 2.] THE SPERMATOGENESIS OF LUMBRICUS. 28 1 



C. Spermatocytes of the Secoitd Order. 



In spermatocytes of the second order there are but sixteen 

 double chromosomes — one-half as many as in the spermato- 

 gonia. After their division the daughter cells, or spermatids, 

 contain sixteen single chromosomes (Figs. 28 and 29). 



The following distinctions may now be drawn between 

 spermatocytes of the first and second orders : in the first order 

 occurs reduction in number of the chromosomes due to chro- 

 matic activity ; this is followed by a reduction in quantity of 

 chromatin through karyokinetic division ; in the second order 

 the chromosomes are passive, while reduction in mass occurs 

 through karyokinetic division. 



D. Spermatids . 



The spermatid nucleus is the result of the double reducing 

 division. It contains only half as many chromosomes as in 

 the spermatogonium. 



After division of the spermatocytes of the second order the 

 chromatin gives rise to a reticulated mass which gradually 

 becomes more and more compact and homogeneous (Figs. 30- 

 33). The spermatid is a small round cell closely attached to 

 the outside of the blastophore (Fig. 6). The archoplasm lies 

 at the extremity furthest removed from the blastophore and is 

 closely applied like a cap to the nuclear membrane (Fig. 35), 

 or lies like an independent cytoplasmic sphere between the 

 membrane and the extremity of the cell (Fig. 6). The cyto- 

 plasm has no other distinctive feature ; it is small in amount 

 and apparently only sufficient to cover a comparatively large 

 nucleus. There is no indication of granules, which are so 

 characteristic of the blastophore at this stage (Fig. 36). 



The mature spermatozoon is developed from the spermatid 

 by a simple metamorphosis. The nucleus elongates, and the 

 distal extremity becomes drawn out to form the tail. 



The first indication of the spermatid metamorphosis is loss of 

 reticulation in the nucleus (Figs. 31, 32). The chromatin be- 

 comes dense and homogeneous, forming at first a rounded mass 

 like a ball lying within the nucleus (Fig. 33), but later becoming 



