GAMETOGENESIS AND SPOROGENESIS 



221 



their migration around it. The chromatic substance is 

 then seen to arrange itself in a layer against the inside of 

 the nuclear membrane, and as spermiogenesis proceeds 

 it abandons the posterior portion and collects as a com- 

 pact, deeply staining cap at the anterior side. As the 

 acrosome begins to form the perforatorium, this chro- 

 matic cap becomes very asymmetrical and the whole 

 nucleus elongates and begins its transformation into the 

 slender sperm head. The "pseudoblepharoplast," 

 which has already been mentioned and which may pos- 

 sibly represent chromosomal material, disappears at 

 about this stage. The head continues to elongate in the 

 form of a narrow spoon with the acrosomic band lying 

 in the hollow; eventually it becomes a slender pointed 

 body in which nucleus and acrosome can no longer be 

 distinguished. During these changes the non-chro- 

 matic constituents of the nucleus gradually diminish 

 and disappear, so that the nucleus of the spermatozoon 

 is an extremely concentrated chromatic mass in which 

 structure can be demonstrated only in rare cases. 



Cytoplasm. — As the other components of the sper- 

 matid undergo the transformation outlined above, the 

 cytoplasmic cell body elongates and remains visible 

 around them (with the possible exception of the tip of 

 the axial filament) until a comparatively late stage. 

 Toward the close of spermiogenesis in the insects it has 

 been ascertained that a cytoplasmic ball, containing the 

 Golgi remnant and other granules of an unknown nature, 

 is sloughed off and ingested by the nutritive epithelial 

 cells lining the spermatic cyst. In other animals a cyto- 

 plasmic mass is likewise eliminated, but the amount of 

 "active" protoplasm contained in it is uncertain. 



The Mature Spermatozoon (Fig. 134). — The mature 

 spermatozoon has two main parts : the head, which is a 

 dense chromatic mass comprising the nucleus, the acro- 

 some, and sometimes a skeletal fiber of uncertain origin; 

 and a tail, consisting of an axial filament produced as an 

 outgrowth from the distal centriole, the thread-like 

 sheaths formed by the chondriosomal derivatives, and 

 an uncertain amount of residual cytoplasm. It is prob- 

 able that a thin cytoplasmic membrane exists about 

 the head also, although this is ordinarily invisible. 

 Koltzoff (1909) was able to demonstrate a membrane in 

 this region by using hypotonic solutions. In A rhacia and 

 Nereis, according to Popa (1927), the sperm head con- 



/-- 



Fig. 134.— Dia- 

 gram of a typica. 

 mammalian sper- 

 matozoon, a, acro- 

 some; n, nucleus; 

 c, proximal centri- 

 ole; c', distal cen- 

 triole and deriva- 

 tives; w, cell mem- 

 brane; d, chondrio- 

 somes; /, axial fila- 

 ment of tail; m, 

 middle piece; p, 

 principal piece of 

 tail; e, end piece of 

 tail. {After Bowen, 

 1924c.) 



