362 



THE GENITOURINARY ORGANS. 



I- a 



structure of both the axial and marginal threads (Ballowitz), while 

 the accessory thread is separated into a number of short segments. 

 In mammalia, and especially in man, the 

 spermatozoa seem to be" more simply con- 

 structed. Here the head is pyriform, and 

 somewhat flattened, with a slight ridge along 

 the depression at either side of its anterior 

 thinner portion (Fig. 289). In some mammalia 

 (mouse), the head is provided with a so- 

 called cap, which corresponds to the lance 

 previously mentioned. The middle piece is 

 relatively long and shows a distinct cross- 

 striation, which may be attributed to its spiral 

 structure. Here also the middle piece is tra- 

 versed by the axial thread, which ends at the 

 head in a terminal nodule, and may be sep- 

 arated as in other mammalia into a number 

 of fibrils. Some years ago Gibbes described 

 an undulating membrane in the human sper- 

 matozoon, an observation which was confirmed 

 by W. Krause (81). The head of the .human 

 spermatosome is from 3 /j. to 5 [i long, and 



from 2 u to 3 u in breadth ; the middle piece 

 Fig. 289. Human ' J ' 



spermatozoa. The two is 6 // long and I fj. in breadth ; the tail is from 



at the left after Retzius 40 // to 60 /J. long, and the end-piece 6 fj. long. 



extreme left ^ seen* in ^he spermatozoa are actively motile, a phe- 



profile; the other in nomenon due to the flagella, which give them 



surface view; the one a S pi ra 1 boring motion. They are character- 



at the right is drawn as , 



described by Jensen -. a, lz ed by great longevity and are very resistant 

 Head ; l>, terminal nod- to the action of low temperatures (vid. Pier- 



ule; c, middle piece; gol g \ j n SQme spedes o f bat the Sper- 

 a, tail ; e, end-piece of . L r 



Retzius. matozoa penetrate into the oviduct of the 



female in the fall, but do not contribute to im- 

 pregnation until the spring, when the ova mature. (For the 

 structure of the spermatosomes see Jensen, Ballowitz.) 



2. THE TESTES. 



The testis is inclosed within a dense fibrous capsule, the 

 tunica albuginea, about one-sixteenth of an inch in thickness, and 

 surrounded by a closed serous sac, derived from the peritoneum 

 during the descent of the testes, and therefore lined by mesothelial 

 cells. This serous sac the tunica vaginalis consists of a visceral 

 layer attached to the tunica albuginea, and a parietal layer which 

 blends with the scrotum. The cavity contains normally a small 

 amount of serous fluid. On the inner surface of the tunica albuginea 

 is found a thin layer of loose fibrous tissue containing blood-vessels 

 the tunica vasculosa. The tunica albuginea is thickened in its 



