REPRODUCTIVE ORGANS, 21 



In a general way, a skeleton performs three functions. 

 Firstly, it gives a general firmness or consistence to the whole 

 body which from its protoplasmic nature would otherwise 

 be mobile. Secondly, it protects the body from enemies, 

 physical or organic, and^ thirdly, it provides a mechanical 

 system of levers through which the muscles can operate. 



Reproductive System. — The vital phenomenon of 

 Growth does not become concentrated in one special sys- 

 tem of organs, though there are striking cases of differential 

 growth in many animals. In the case of Reproduction it 

 is different, and a special reproductive system appears very 

 early in the animal kingdom. The subject of reproduction 

 is dealt with under Embryology, but we may note here that 

 reproductive organs usually have : — 



1. The primary go?iad^ producing the germ -cells. The 

 male organ is called the testis, the female the ovary. 



2. Ducts leading to the exterior. The male duct is 

 called the vas deferens, the female the oviduct. 



Further differentiations ensue as development becomes 

 more complex. Firstly, the eggs are supplied with yolk 

 and yolk-glands are often required. Secondly, the eggs 

 require protecting shells or capsules produced by shell-glands. 

 Thirdly, these additions require internal fertihsation, within 

 the oviduct, before the shell is added. This means copula- 

 tion and a copulatory organ in the male, whilst there may 

 be a receptacle for the semen {receptaculum seminis) in the 

 female. Lastly, the eggs and young may be retained for 

 some time within the oviduct of the female, in which case 

 the portion of the oviduct adapted for this purpose is the 

 uterus. Various accessory glands may become superadded. 

 We may tabulate the reproductive organs as follows : — 

 Alale I. Production of spermatozoa Testis.' ' 



2. Transportation to exterior Vas deferens. 



3. Introduction of same into female, Penis... 

 Fejuale . . . i . Production of eggs Ovary. • ■ 



2. Transportation of eggs to exterior, Oviduct. [glands. 



3. Production of yolk and shell Yolk-glands and shell- 



4. Reception of sperms Receptaculum seminis. 



5. Retention of egg and embryo Uterus. 



