56 



THE HYDRA. 



Let the reader imagine that he has cut off from 

 the small quill of a pigeon's feather about three- 

 eighths of an inch, and he will have before him the 

 shape and size of the green hydra, discovered by 

 M. Trembley, and which may still be found in 

 weedy ponds, or slowly running streams. Until 

 very recently, a hydra was described as a small 



SECTION OF THE BR,OW]\~ HYDRA HYDRA TUSCA. 



living tube, presenting to the eye merely a gelati- 

 nous substance, in which small grains are intermixed. 

 But M. Gervais has studied one of these creatures 

 with all the present advantages of microscopic 

 power, and shows that it is more complex than has 



