TESTIS 



337 



The protoplasm of the spermatid forms an elongated mass at the pos- 

 terior end of the nucleus. It contains the centrosome which soon divides 

 in two. Of these the anterior forms a disc which becomes adherent to 

 the nuclear membrane. The poste- 

 rior centrosome also becomes a disc 

 after giving rise to a motile axial 

 filament, which grows out from it like 

 a cilium. The disc-like centrosome 

 attached to the anterior end of the 

 filament becomes thin in such a way 

 that its peripheral portion is detached, 

 and as a ring surrounding the fila- 

 ment it passes to the posterior limit 

 of the protoplasm. The protoplasm 

 between the two parts of the poste- 

 rior centrosome is reduced to a thin 

 layer in which a spiral filament de- 

 velops, winding about the axial fila- 

 ment. Distal to the centrosome ring, 

 the axial filament, which consists of 

 fine fibrils, is surrounded by a thin 

 membrane, which terminates or be- 

 comes very thin near the extremity 

 of the filament. This membrane, 

 which in salamanders forms a conspicuous undulating frill, is thought to 

 be a product of the filament and not an extension of the protoplasm. 

 In man it is inconspicuous, and many of the details here described can 

 be made out only 'under most favorable conditions. The preceding ac- 

 count is based on studies of the guinea-pig (Meves, 

 Arch. f. mikr. Anat., 1909, vol. 73, pp. 751-792). 



Mature spermatozoa are divided into three 

 parts the head, neck, and tail. The head (3-5 /z 

 long and 2-3 /* wide) includes the nucleus, galea 

 capitis and perforatorium. The neck consists of 

 the anterior centrosome and the substance, not 

 traversed by the axial filament, between it and 

 the posterior centrosome. The neck in man is 

 not constricted as in some forms, yet it is a place 

 where the head may become detached. The tail 

 includes three parts, the connecting piece, chief piece 



and end piece. The connecting piece (6 n long and scarcely i /* wide) 

 consists of protoplasm, axial and spiral filaments, and the two parts of 

 the posterior centrosome. The chief piece (40-60 /* long) is the axial 



FIG. 336. DIAGRAMS OF THB DEVELOPMENT OF 

 SPERMATOZOA. (After Meves.) 



a. c., anterior centrosome; a. f., axial filament; 

 c. p., connecting piece; ch. p., chief piece; g. c., 

 galea capitis; n., nucleus; nk., neck; p., pro- 

 toplasm; p. c., posterior centrosome. 



FIG. 337. SPERMATOZOA: i, 



2, 3, HUMAN 4, FROM A BULL. 



a, Head; b, connecting piece, 



and c, chief piece of the 



tail. i ( 3, and 4, Surface 



views; 2, side view. X 360 



