562 THE HUMAN BODY 



tional mitosis in ovum and polar body just as in the sperm formers. 

 The polar body divides into two of equal size. The division of 

 the ovum is again unequal, and an additional polar body is formed. 

 At the end of maturation of the egg, therefore, we have four cells 

 corresponding to the four sperm, but one of them has retained 

 virtually all the cell substance, and is the functional ovum. Figure 

 150 is a diagram illustrating the stages of maturation. The ovum 

 and the sperm each contain half the original number of chromo- 

 somes. When they fuse in the process of fertilization the full 

 number is restored. 



Accessory Reproductive Organs. The organ in which ova are 

 produced is known as the ovary, that forming spermatozoa, as 

 the testis or testicle; but in different groups of animals many addi- 



- -Ovarian .egg. 



**"** 



polar body. 

 Second polar body (abortive ovum). 



FIG. 150. Diagram showing the genesis of the egg (after Boveri). A similar 

 diagram in which all the daughter cells were of equal size would serve to illustrate 

 the genesis of spermatozoa. 



tional accessory parts may be developed. Thus, in all but the 

 very lowest Mammalia, the offspring is nourished for a consid- 

 erable 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 va- 

 gina; and two tubes, the oviducts or Fallopian lubes, convey the 

 eggs to it from the ovaries. In addition, mammary glands provide 

 milk for the nourishment of the young in the first months after birth. 

 In the male mammal we find as accessory reproductive organs, vasa 

 deferentia which convey from the testes the seminal fluid contain- 

 ing spermatozoa; vesicular seminales (not present in all Mammalia), 

 glands whose secretion is mixed with that of the testes or is ex- 

 pelled 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 fertilizing liquid is conveyed into the vagina of the female. 



