362 



THE GENITOURINARY ORGANS. 



d 



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 // to 5 fj. long, and 

 from 2 fji to 3 ft in breadth ; the middle piece 

 is 6 IJL long and I p in breadth ; the tail is from 

 40 fj. to 60 p. long, and the end-piece 6 p long. 

 The spermatozoa are actively motile, a phe- 

 nomenon due to the flagella, which give them 

 a spiral, boring motion. They are character- 

 ized by great longevity and are very resistant 

 to the action of low temperatures (vid. Pier- 

 In some species of bat the sper- 

 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.) 



Fig. 289. Human 

 spermatozoa. The two 

 at the left after Retzius 

 (8 1) ; the one at the 

 extreme left is seen in 

 profile ; the other in 

 surface view ; the one 

 at the right is drawn as 

 described by Jensen : a, 

 Head ; b, terminal nod- 

 ule ; c, middle piece; SQ j o~\ 

 d, tail ; e, end-piece of 

 Retzius. 



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 



