236 



MANUAL OF HISTOLOGY. 



FIG. 106. Seminal elements of 

 man: , undeveloped; &, mature. 

 St. George. 



They are as follows 



The shape of the head is pyriform, the broad part being con- 

 nected with the body ; each has an average length of 0.0045 

 mm., and its breadth is about half as much. The middle por- 

 tion or body is about 0.0061 mm. long, while the tail measures 



about 0.0406 mm. Both the body and 

 head of the seminal elements seem to 

 be rigid, the terminal thread or tail 

 having an active motion. From this 

 description it will be seen that a com- 

 parison of its structure with that of a 

 ciliated epithelial cell is admissible, and 

 indeed quite reasonable. 



The way in which spermatozoa are 

 formed is still imperfectly known, and 

 two different views claim our attention. 

 a. The nucleus of the seminal cells 

 moves to the periphery, then at the opposite side the proto- 

 plasm of the cell is elongated into a caudal appendage ; the 

 nucleus continuing to advance causes the protoplasm to be- 

 come more and more elongated, and it is ultimately lengthened 

 into a thread-like tail, while the nucleus, with its thin layer of 

 protoplasm, constitutes the head. b. In this view the columnar 

 or prismatic-shaped cells, the most external layer of cells fill- 

 ing the seminal tubules, are thought to be the spermatozoa- 

 producing elements. The inner .remaining cells of the tu- 

 bules experience no further development. During the active 

 stage of the gland the spermatic cells become elongated, and 

 extend into the centre of the tubule ; their free extremities 

 become enlarged, and have a number of buds or club -like pro- 

 jections, eight to twelve, developed upon them. In each bud 

 is formed a nucleus ; these nuclei eventually become the 

 heads of spermatozoa, and the protoplasm is further developed 

 into the body and tail. The cells from which the spermatozoa 

 have their origin are named spermatoblasts. 



Klein, in his recent "Atlas of Histology," gives a very ex- 

 tended description of the development of spermatozoa. Ac- 

 cording to this writer there are several layers of epithelial 

 cells lining the inside of the membrana propria of the seminal 

 tubules. These layers he divides into an outer and inner. 

 The outer, situated next to the membrana propria, embraces 

 the germ-cells of Sertoli. The inner layer, those nearer the 



