PART III 



SECTION XII 

 REPRODUCTION 



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 sperma- 

 tozoa, the ovary 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 vas 

 deferens has not this effect. 



The genital gland in both sexes is formed from a longi- 

 tudinal thickening or ridge at the posterior part of the 

 coelom 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 around it to form the zona granulosa, the whole 



group constituting a Graaiian follicle. 



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