Kidney - 



Ureter- 



Vas deferens 



Testis 



FRIEDIv;aN 



-Kidney 



Ureter 



■Vcis deferens 



-Testis 



Urethra 



AAALE REPRODUCTIVE ORGANS IN MAMMALS 



The sperm cells originate in the linings of fine twisted tubules that make up the mass 

 of each spermary (testis). The seminal fluid accumulates in small reservoirs, the seminal 

 vesicles. The tubes run together into common ducts leading into the urethra, which 

 also carries urine from the bladder 



until the young are able to swim. Among the clams the eggs are discharged 

 into the mantle cavity, where they are fertilized by sperms swimming in the 

 water that circulates there (see illustration, p. 209). 



Reproducdon in Coelenterates^ In the hydra and its relatives the indi- 

 vidual polyps attach themseKes at the base of the stalk. In some forms they 

 remain permanently attached, in others only temporarily. In most species 

 the stalk puts out buds, which become new polyps. In this way a colony of 

 countless branches is formed, each one ending in a polyp — as in coral colonies. 



Among some of the species related to the hydra and the sea anemones there 

 is a regular alternation between a generation that reproduces sexuall} — that 

 is, by means of conjugating gametes — and a generation that reproduces by 

 budding, or without sex (see illustration, p. 384). 



Two Kinds of Generations" Since many species of plants and animals 

 reproduce vegetatively, or by means of spores, as well as sexually, we may 

 wonder whether the individuals that reproduce in these two different ways 



iSee No. 10, p. 396. 



-SeeNos. 11 and 12, p. 396. 



382 



