272 HISTOLOGY. 



the protoplasm. The protoplasm between the two parts of the posterior 

 centrosome is reduced to a thin layer in which a spiral filament develops, 

 winding about the axial filament. The axial filament, which consists of 

 fine fibrils in some forms at least, distal to the centrosome ring is sur- 

 rounded by a thin membrane which terminates or becomes very thin 

 near the extremity of the filament. This membrane which in salaman- 

 ders 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 incon- 

 spicuous. In fact most of the detail which is seen in ordinary sections 

 containing spermatozoa is shown in Fig. 308. 



Mature spermatozoa are divided into three parts, the head, neck, and 

 tail. The head (3-5 /< long and 2-3 // wide) includes the nucleus, galea 

 capitis and perforatorium. The neck consists of the anterior centro- 

 some and the substance, not traversed by the axial filament, between it 



Spermatid. 



Nuclei of sus- 

 tentacular cells 



n * 



MS, 



^L f '' ^- ; & $-\ Sperma- 

 f^^^^'^BteBl^fc^J togonium. 



^ 







Interstitial con- 

 nective tissue. 



FIG. 309. FROM A LONGITUDINAL SECTION THROUGH A CONVOLUTED TUBULE 

 OF A HUMAN TESTIS. X 360. 



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 // long and scarcely i // wide) consists of proto- 

 plasm, axial and spiral filaments and the two parts of the posterior cen- 

 trosome. The chief piece (40-60 /< long) is axial filament with a surround- 

 ing membrane, and the end piece (10 /i) is a prolongation of the filament. 

 In the convoluted tubules the heads of the spermatozoa are attached to, 

 or buried in the protoplasm of the sustentacular cells which are supposed 

 to nourish them. Their tails project into the lumen. Later they become 

 detached and float in the albuminous fluid secreted in small quantity by 

 the tubules. They pass through the straight tubules and rete to the epi- 

 didymis, in which they accumulate and where they first become motile. 

 Their motility is greater, however, in the seminal fluid which is a mix- 



