MATURATION. 



19 



each dyad (Fig. 10, 7, K, L). A primary spermatocyte gives rise therefore to 

 four spermatids in which the number of chromosomes is reduced to one-half 

 the normal (Fig. io,Z). 



After the last spermatocyte division and the resulting formation of the 

 spermatid, the nucleus of the latter acquires a membrane and intranuclear net- 



FIG. 10. Reduction of chromosomes in spermatogenesis in Ascaris megalocephala (bivalens). 

 Brauer, Wilson. A G, Successive stages in the division of the primary spermatocyte. The original 

 reticulum undergoes a very early division of the chromatin granules which then form a doubly split 

 spireme (5). This becomes shorter (C), and then breaks in two to form the 2 tetrads (D, in p'rofile, 

 E, on end). F, G, H, First division to form 2 secondary spermatocytes, each receiving. 2 dyads. /, 

 Secondary spermatocyte. /, K t The same dividing. Z,, Two resulting spermatids, each containing 

 2 single chromosomes. 



work, thus passing into the resting condition. Without further division the 

 spermatid now becomes transformed into a spermatozoon. This is accomplished 

 by rearrangement and modification of its component structures (Fig. 1 1). The 

 ccntrosome either divides completely, forming two centrosomes, or partially, 

 forming a dumb-bell-shaped body between the nucleus and the surface of the 



