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THE SCIENCE OF LIFE. 



sented by the Hydra, and the latter by the Sea-anem- 

 one, or Actinia. 



The Hydra is named after a fabled monster that re- 

 produced its heads as fast as they were cut off. The 



genus comprises two species, 

 the green and the brown 

 Hydra, (H. viridis and H. 

 fusca.) (Fig. 74.) They are 

 minute creatures, about a 

 quarter of an inch long, gen- 

 erally found on the under 

 surface of aquatic plants, at- 

 tached by a disk, while their 

 long tentacles float down- 

 ward in search of prey. The 

 body is a simple tube, or 

 cavity, and the tentacles 

 are supplied with " lasso- 

 threads," or nettling thread- 

 cells. In the early summer 

 small buds grow from the 

 base of the body, which grow 

 into the likeness of the par- 

 FIG. 74 .-Hydra fusca, with a young bud ent, and then are detached. 



at b. and a more advanced bud at c. o . , / 



Sometimes a second crop 01 



buds arise from the first before it is separated. Later in 

 the season eggs form from modified cells of the inner 

 layer, which burst through the outer layer, become free, 

 and develop into new Hydrae. 



These animals are nearly allied to the Protozoa, since 

 the differentiation of function in the bioplasts is incom- 



