THE MALE FUNCTION 
17 
II. Mammals 
We are now prepared to study reproduction in the highest 
group of animals, the mammals, those which nourish their 
young with milk. We have seen that sexual reproduction is 
superior to asexual in bringing variety and vigor to the cell. 
We have noted the value of cross fertilization, the many de¬ 
vices for securing it, and the impossibility of close fertiliza¬ 
tion when the egg cell and the sperm cell are produced in 
individuals of different sex. We have discussed the methods 
of- fertilizing the ovum and the provision nature makes for 
maintaining the life of the embryo. It now remains to see 
Figure 13. — Human Spermatozoon. 
Seen from two aspects, magnified about 2000 times. 
how these principles are applied in detail in the highest 
animals. 
The Male Function. — The work of the male is to produce 
and bring to the female the spermatozoa, and to aid in pro¬ 
tecting and feeding her and the offspring. The spermatozoa 
are produced in a pair of organs called testes (tes'tes). The 
testes consist mainly of many coiled tubes whose lining cells 
undergo division. The separated half of the divided cell 
splits into spermatozoa each of which contains half the full 
number of chromosomes. The spermatozoa from all the 
tubes of each testis are gathered into the main tube or duct 
which passes from the testis over the pubic bone and behind 
the bladder, opening just below the bladder into the urethra, 
the tube through which urine is discharged. 
