4 THE HUMAN BODY. 



individuals; such a mode of reproduction is called parthen- 

 ogenesis: but in the majority of cases, and always in the 

 higher animals, this is not so; the fusion of two cells, or of 

 products of two cells, is a necessary preliminary to develop- 

 ment. Commonly the coalescing cells differ considerably in 

 size and form, and one takes a more direct share in the 

 developmental processes; this is the egg-ceil or ovum; the 

 other is the sperm-cell or spermatozoon. The fusion of 

 the two is known as fertilization. Animals producing both 

 ova and spermatozoa are hermaphrodite; those bearing ova 

 only,, female; and those spermatozoa only, male: hermaphro- 

 ditism is not found in Vertebrates, except in rare and 

 doubtful cases of monstrosity. 



Accessory Reproductive Organs. The organ in which 

 ova are produced is known as the ov&ry, that forming 

 spermatozoa, as the test-is or testicle; but in different groups 

 of animals many additional accessory parts may be devel- 

 oped.] Thus, in Mammalia, the offspring is nourished for a 

 considerable portion of its early life within the body of its 

 mother, a special cavity, the uterus or womb, being provided 

 for this purpose: the womb communicates with the exterior 

 by a passage, the vagj.na; and two tubes, the oviducts 

 or Fallopian tubes, convey the eggs to it from the ovaries. 

 In addition, mammary glands provide milk for the nour- 

 ishment of the young nTthe first months after birth. In 

 the male mammal we find as accessory reproductive organs, 

 vasa deferentia, which convey from the testes the seminal 

 fluid containing spermatozoa; vesiculm seminales (not pres- 

 ent in all Mammalia), glands whose secretion is mixed 

 with that of the testes or is expelled after it in the sexual 

 act; a prostate gland, whose secretion is added to the 

 semen; and an erectile organ, the penis, by which the fer- 

 tilizing liquid is conveyed into the vagina of the female. 



The Male Reproductive Organs. The testes in man 

 are paired tubular glands, which lie in a pouch of skin called 

 the scrotum. This pouch is subdivided internally by a par- 

 tition into right and left chambers, in each of which a testicle 

 lies. The chambers are lined inside by a serous membrane, 

 the tunica vaginalis, and this doubles back (like the pleura 



