CHAPTER XXXII. 

 REPRODUCTION. 



The most important function of an animal's life is the produc- 

 tion of a new individual which in all peculiarities of function and 

 structure is essentially like the parent. The fundamental prob- 

 lems of the process of reproduction which are of physiological 

 importance, are those of fertilization and heredity. Fertiliza 

 tion consists in the union of two parent cells to produce a new 

 cell which is endowed with the power of growth and subdivision. 

 Heredity refers to the phenomenon which directs the cell thus 

 fertilized to develop into an individual like its parents. 



Since up to the present time most of our knowledge of these 

 processes is based on anatomical data, we will discuss them very 

 briefly and will pay more attention to what we may term the 

 accessory phenomena of reproduction, which are of more practi- 

 cal interest at present. 



Reproduction in the unicellular animals is a simple process. 

 The parent cell divides exactly in halves and two daughter cells 

 are produced. In the multicellular animals this type of repro- 

 duction is impossible and the process is delegated to a portion 

 of the animal's body known as the reproductive system. This 

 system in man includes the specialized tissues which produce the 

 cells or eggs from which the new individual develops, and the 

 accessory organs which are concerned in providing favorable 

 conditions for the development of these cells. 



Fertilization. A very simple type of fertilization's seen in 

 unicellular animals, which ordinarily reproduce by simple divi- 

 sion. After a series of simple divisions the cell becomes unable 

 to develop more cells until after it has united with another cell 

 to form one large cell. This process is termed conjugation. In 

 higher forms, the development of the egg is always preceded by 

 the phenomenon of fertilization, which is somewhat similar to 



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