REPRODUCTION. 



179 



How is the seminal fluid conveyed from the testis? 



The seminiferous tubules all converge toward the epididymis, 

 a tortuous tubule which is lined with mucous membrane, and lies 

 beside the testis in a long, convoluted mass which may be unrav- 

 elled, and is found to be about 20 feet long. This empties its con- 

 tents, or rather continues on, in the vas defer ens, which conveys the 

 semen to the seminal vesicles. During this passage the mucous 

 membrane adds a viscid mucous secretion in which the spermato- 

 zoa are liberated and, so to speak, diluted. 



What is the appearance of the spermatozoa ? 



In the seminiferous tubules the developing spermatozoa may be 

 seen with the heads all united in the cells from which they arise, 

 the tails projecting brush-like into the cavity of the 

 tube. But they are soon separated. They then con- 

 sist of a head and a tail (Fig. 55). In length they 

 are about 3 ^ to ^ of an inch. The head is some- 

 what elliptical and the tail gradually tapers. In other 

 animals than man the size and form vary from those 

 of man, though in a general way they conform. 



What action of the spermatozoon permits it to enter 

 the uterus and Fallopian tube? 



There is a very active vibratory motion of the tail 

 of the spermatozoon, which allows it quite free motion 

 in a fluid medium. It is by this swimming motion, in 

 which it may be compared to a tadpole, that the semi- 

 nal cells are able to reach the ovum against the action 

 of the cilia in the uterus and Fallopian tube. 



Is a single spermatozoon sufficient to fecundate an 



ovum? 



It probably is. There have been more than one seen 

 in an impregnated ovum, but it is probable that only 

 one enters into the formation of the male pronucleus, 

 the rest remaining inactive. 



Where is the ovum impregnated ? 

 In the Fallopian tube. 



What leads us to the conclusion that the egg is fecundated in 



the Fallopian tube ? 

 (1) The spermatozoa are found there. (2) Before the ovum 



I urn an Sper- 



1, in profile ; 

 2, viewed on 

 the flat; 6, 

 head ; c, mid- 

 dle-piece ; <1, 

 tail ; e, end- 

 piece of the 

 tail. 



