The Reproductive System 259 



these ducts aid its movements. The secretions of the seminal vesicles, 

 prostate, and Cowper's glands are gradually added, and the semen thus 

 is formed. 



Sperm are first produced at puberty, and are then produced con- 

 tinuously throughout the lifetime of the individual. At puberty, their 

 production is accompanied by several changes which are apparently 

 brought about by the endocrine secretions of the interstitial cells of the 

 testes. These accompanying changes include such things as the lower- 

 ing of the voice and the appearance of heavier hair on the face. 



THE FEMALE REPRODUCTIVE SYSTEM 



Just as all animals but the protozoans have testes for the produc- 

 tion of sperm, they also have special structures for the production of the 

 eggs, the ovaries. Similarly, forms such as the sponges and coelenterates 



ovary 



uferys 



large intestine 



vagino 



labium major 



anus 



Fig 77 —The female reproductive system. (By permission from Man and 

 the Biological World, by Rogers. Hubbell, and Byers, 1952. McGraw-Hill Book 

 Company. Inc.) 



shed the eggs directly into the surrounding medium. Fertilization and 

 development are dependent upon chance. Most of the animals above 

 these forms have progressively greater assurances for the fertilization 

 of the eggs and at times for the care of the young. The mammals again 

 show the culmination of this development of specialized structures. 



