REPRODUCTION 



AND 

 DEVELOPMENT 



IN 

 CHORDATES' 



CHAPTER 



5 



Living organisms are distinguished by the capacities of metaboHsm, respon- 

 siveness, and reproduction. The primary effect of the activities of the organ 

 systems that are speciaUzed to provide the metabolic requirements of cells and 

 to coordinate the functions of all parts of the organism is to maintain the life 

 of the individual. The individual also exists as the potential parent of a new 

 generation of his species. As a result of the capacity of reproduction certain 

 cells can become detached and, either alone or after union with cells of an- 

 other organism of the same kind, can give rise to a new individual capable 

 of becoming like the parent or parents in all essential respects. Reproduc- 

 tion, like metabolism and responsiveness, is dependent on a cellular mechanism, 

 and a specialized organ system is related to this activity of the individual. 



The Reproductive System 



The reproductive system of vertebrates consists of the reproductive organs, 

 or gonads, in which the germ cells become differentiated, and the reproduc- 

 tive ducts, through which the germ cells leave the body. During the develop- 

 ment of the individual, the reproductive and urinary systems arise in close 

 association, so that structurally they form what is known as the urinogenital 

 system (p. 57). The functions of the two parts of this system are entirely 



'The group of animals called the chordates includes the vertebrates and their near relatives 

 (p. 217). 



128 



