146 THE MICROSCOPE. Oct. 



To procure this animal, take in a vessel some duck- 

 weed from a ditch or pond of stagnant water. Put this 

 in a receiving glass and cover the glass with a thick 

 paper, leaving a vertical opening on one side. The next 

 day, take off the covering and look at the under side of 

 the weeds. A large number of white roots will be seen 

 extending into the water. Among these the polyps will 

 be found. They are quite in their element here. Their 

 arms and bodies mingle with the filaments of the roots, 

 which, on account of their resemblance, serve as a means 

 of protection. The hydra hold themselves rigid, head- 

 downward, their arms hanging like a woman's hair (fig 

 1), in such a way as to be easily mistaken for the roots 

 of the Lemna. As they prefer the light they are found 

 in the most highly lighted part of the receiving jar. 

 The floating leaves are also on this side. Our little con- 

 trivance is quite useful, for by it one knows in advance 

 just where to find the polyp. 



Take the hydra by breaking off the plant to which 

 they are attached, being careful not to destroy the arms, 

 which are sometimes attached by their free extremities 

 to surrounding objects. These arms (fig. 2), are very 

 extensible and can be contracted or elongated in the 

 same individual. The number of arms is not always six, 

 as it is generally believed, but, unless in case of accident, 

 it is at least six; it may be more, but usually some mul- 

 tiple of six. 



The hydra has a foot terminated by a hollow disk, by 

 means of which it can attach itself to bodies in the water 

 as well as to aquatic plants. It is found attached to 

 stones or stakes standing in the water, to bits of wood, 

 or strings and ropes floating in the water, also to fishing 

 nets. The foot is solid and is terminated by a hollow 

 body which is shaped like the finger of a glove, having 

 but a single opening. This cavity acts at the same time 

 as a stomach and an intestine. Its opening is at once 



