336 



HISTOLOGY 



spermatozoa may be gathered in characteristic clumps at their upper ends 



(Fig. 332). 



In ordinary sections of the testis, the sustentacular cells may be recog- 

 nized by their distinctive nuclei (Fig. 335). The sexual cells in the basal 

 row are presumably spermatogonia. Above them are the spermatocytes, 

 which are larger; their nuclei usually show spiremes or other indications 

 of cell division. Secondary spermatocytes are further out than the pri- 

 mary spermatocytes; and above them are the spermatids in various 

 stages of transformation into spermatozoa. Since spermatogenesis occurs 

 in "waves," the outer cells in a tubule cut lengthwise form a succession of 

 zones, each of which shows gradations from young spermatids to mature 

 spermatozoa; a single zone is included in Fig. 335. In transverse sections 

 all the superficial cells may be of one stage, which differs from that in 

 the adjoining tubule (Fig. 332). 



Heads of 

 spermatozoa. 



Spermatocyte. 



Crystalloids in 

 interstitial 

 cells. 



.,**?" 



f 'lfr&- A" 





**- <r- 



"N. 



a : 



Spermatid. 



Nuclei of sus- 

 tentacular cells. 



Interstitial con 

 nective tissue. 



FIG. 335. FROM A LONGITUDINAL SECTION THROUGH A CONVOLUTED TUBULE OF A HUMAN TESTIS. X 60 



Stages in the transformation of a spermatid into a spermatozoon are 

 shown in the diagram Fig. 336. The chromosomes of the spermatid 

 disappear in a dense chromatic network which becomes apparently homo- 

 geneous. This deeply staining nucleus passes to one end of the protoplasm 

 of the spermatid. It becomes the essential part of the head of the sper- 

 matozoon, which in man is a flattened structure, oval on surface view, 

 and pyriform with its apex forward when seen on edge (Fig. 337). The 

 head is at the anterior end of the spermatozoon, which during its develop- 

 ment is directed toward the basal layers of the convoluted tubule. The 

 anterior end of the head is probably covered by a thin layer of protoplasm, 

 known as the galea capitis. The archoplasm of the spermatid (known as 

 the idiozome) is said to leave the centrosome and to enter the protoplasm 

 of the galea capitis, where it forms the perforatorium. If this exists in 

 man, it is in the form of a cutting edge following the outline of the front 

 of the head; in other animals the perforatorium may be a slender spiral 

 or barbed projection, which enables the spermatozoon to penetrate the 

 ovum. 



