THE HYDRyE, OR POLYPES. 15 



figs. 3, 65 7). — The body is of a brownish colour, and its 

 lower half much more slender than the upper part. The 

 arms are, in general, from six to eight in number, and 

 several times longer than the body. 



Fig. 3, an individual with the arms fully extended in 

 quest of prey. A red worm (c), and a small water in- 

 sect (d), are seen captured by the tentacula. 



Fig. 6, a polype bending its body, and throwing about 

 its arms in an undulating manner in search of food. 



Fig. 7, a red worm partly drawn into the stomach of 

 a polype, being too large to be swallowed entire. 



Fig. 8, a vertical or longitudinal section of a polype, 

 highly magnified, to shew the internal structure: e, the 

 cellular tissue, which forms the constituent substance of 

 the entire animal; y^ the tubular arms; g, the inner sur- 

 face of the digestive sac. 



The Hydra, when taken out of the water, shrinks into 

 a small round mass, which, examined under the micro- 

 scope, is seen to be composed of cells, and of greenish or 

 reddish brown granules, loosely connected by a glairy 

 mucus. The cells are condensed on the external surface, 

 so as to constitute a double layer of integument; but 

 the lining of the cavity of the body is made up of cells 

 that are transversely elongated, and forms a surface which 

 is covered with exceedingly minute eminences, termed 

 villi, from the resemblance to the pile of velvet. 



