SEX IN" LIVING FOKMS 101 



intestines. From the head grows out a body, which 

 shortly divides into segments, which gradually increase 

 in number and size. Each section contains both male 

 and female sexual organs, and is self-fecundating. 

 After a time, the older segments become detached, and 

 lead independent lives, until all the ovules they contain 

 have been deposited. It has been established that more 

 than twenty thousand eggs are produced by a single 

 worm. 



In higher orders of animals, fecundation takes place 

 within the generative passages of the female by contact 

 between the male and female organs. To effect this, 

 there are necessitated certain accessory organs, the 

 penis in the male and the vagina in the female. 



Nothing in all the range of nature is more remark- 

 able than the adaptation of the two varieties of sexual 

 organs in each species. This necessary provision is 

 both a powerful means of securing the perpetuation 

 of the species, and an almost impassible barrier against 

 amalgamation. 



The act of union, or sexual congress, is called coitus, 

 or copulation. It is accompanied by a peculiar nervous 

 spasm, due to the excitement of special nerves princi- 

 pally located in the penis in the male, and the clitoris 

 and vagina in the female. The nervous action referred 

 to is more exhausting to the system than any other to 

 which it is subject. 



Union of the Ovum and Zoosperm.— The zoosperms 

 not only come in contact with the ovum, but penetrate 

 the thin membrane which incloses its contents, and 

 enter its interior, where they disappear, becoming 

 united with its substance. In the ova of certain fishes, 

 small openings have been observed, through which the 

 spermatozoa find entrance. Wliether such openings 



