HYDEA 61 



IV. Reproduction. The various species of Hydra undergo 

 both asexual and sexual reproduction. The asexual method is 

 by budding. In this process, a portion of the body wall bulges 

 out and increases in size until a sac-like bud is formed. The 

 ectoderm, entoderm, and cavity of the bud are continuous with 

 those of the parent. In the early stages tentacles and a mouth 

 are lacking but these soon appear and the bud is recognizable 

 as a new Hydra attached to the body of its parent. Ultimately 

 the bud breaks away and becomes independent. 



In the sexual method, the ectoderm of certain regions of the 

 body forms spermaries and ovaries which contain the repro- 

 ductive cells. After an egg is fertilized a resistant membrane 

 is formed around it. After some time the fertilized egg is 

 dropped from the surface of the body. It finally undergoes 

 cleavage and gives rise to a new Hydra. 



V. Experiment. Run a little methylen blue under the 

 coverglass. This acts as a chemical stimulus, causing the nem- 

 atocysts to be shot out and at the same time stains them blue. 

 If threads are not shot out from the surface of the body upon 

 contact with the stain, tap lightly with a dissecting needle 

 upon the coverglass immediately above the Hydra. Make out at 

 least two kinds of nematocysts. Draw an 'exploded' specimen 

 of each. The sac of the larger should be 10 mm. in diameter. 

 In the exploded condition, the nettling cells have been com- 

 pletely separated from the body so that each nematocyst may be 

 seen to consist of a long thread-like tube, one end of which is 

 attached to a small sac-like structure. Often some of the nem- 

 atocysts which are discharged from the body are more deeply 

 stained and more irregular in outline than the others. Such a 

 nematocyst is surrounded by its cfiklohlast, the cell which forms 

 the nematocyst. 



REFERENCE 



Hegner, R. W., 1916. An Introduction to Zoology. Macmillan, 



N. Y. 

 Hyman, Libbie H., 1928. Miscellaneous Observations on Hydra, 



with special reference to Reproduction. Biol. Bull., 



44 :65-108. 



