PART III 



SECTION IX 



BEPKODUCTION 



So far the animal has been studied simply as an individual. 

 But it has also to be regarded as part of a species, as an entity 

 which has not only to lead its own life, but to transmit that 

 life to offspring. 



The various problems of reproduction have been already 

 studied by the student in connection with biology, and it is 

 here sufficient to indicate some of the main points in the 

 physiology of the process in mammals. 



(The structure of the organs of reproduction must be studied 

 practically.) 



While the individual is actively growing, the reproductive 

 organs are quiescent ; but .when puberty is reached, they begin 

 to perform their functions the testes to produce spermatozoa, 

 the ovaries to produce mature ova. 



The removal of the sexual organs in the young animal leads 

 to arrest in the development of the special sexual characters, 

 especially in the male, in which these characters are generally 

 best marked. Simple ligature of the vasa deferentia has not this 

 effect, although the tubules of the testes do not develop, and 

 it therefore seems that the interstitial cells of the organs 

 produce a hormone which causes the development of the sex 

 characteristics. 



The genital gland in both sexes is formed from a longitudinal 

 thickening or ridge at the posterior part of the crelom or 

 peritoneal cavity. Over this ridge the endothelium thickens 

 and becomes epithelial-like in structure. Groups of cells grow 

 down into the tissue below. 



In the ovary one of these cells in a group takes a central 

 position and forms the ovum, while the other cells get arranged 



