20 HYDRA 



C. Reproduction. 



Hydra reproduces asexually and sexually. 



1. Asexual reproduction. 



a. Gemmation or budding consists in the formation 



of a hollow outgrowth from the side of the body, 

 which acquires a mouth and tentacles at its distal 

 end, and ultimately constricts at its base, separates 

 from the parent, and becomes an independent 

 animal. 



The rate of budding depends largely on the 

 supply of food and on temperature. If a rapidly 

 budding Hydra be transferred to water in which 

 there is little or no food to be obtained the forma- 

 tion of the buds will be stopped, and buds already 

 formed may even be absorbed. 



A single Hydra may give rise to more than 

 one bud at once, and these may develop secondary 

 buds before separating from the parent animal. 

 In this way temporary colonies may be formed, 

 which, however, sooner or later break up into 

 their component units. 



b. Fission. A Hydra may be cut in two, and each half 



will live and become a perfect animal. The process 

 of fission, however, is not known to occur naturally. 



2. Sexual reproduction. 



Hydra is hermaphrodite, the same animal having 

 both testes and ovaries. Contrary to the rule among 

 hermaphrodite animals, the reproductive organs are 

 extremely simple in structure, and the animals are 

 capable of fertilising their own ova. 



a. The testes are conical or spherical swellings of the 

 body-wall varying in number from one or two up 

 to twenty. They are usually placed near the 

 oral or distal end of the body, not far below the 

 tentacles ; but when numerous they may extend 

 along the greater part of the length of the body. 



