USE OF THE MICROSCOPE IN ZOOLOGY. 49 



one having an immense quantity of extremely fine 

 bristles. As the animal protrudes itselt out of its case, 

 these hairs appear in a dense mass, but soon the lobes 

 separate, and the tufts of bristles on each spread them- 

 selves out in a graceful fan-like torm. What is the 

 use of these long bristles ? I am unable to tell you. 

 Although the animal is destitute of the ciliary wheel- 

 like wings that characterise the Rotifera generally, its 

 whole organisation, and the mechanism and functions 

 of the grinding jaws or gizzard, clearly indicate its 

 relationship with that class ot animals. We must not 

 linger more on these and similar exquisite little forms 

 of animal life ; let me direct your attention to a very 

 strange-looking creature called the Hydra, of which 

 genus there are three well-marked British species 

 namely H. viridis, H. vulgaris, and H.fusca. The first 

 is of a beautiful grass-green colour, the second and third 

 of a pale brown, sometimes nearly white. The arms or 

 tentacles of the last-named species are very long. These 

 animals are found only in fresh water, and generally 

 such as flows very slowly or is quite still. As you will 

 find the study of these creatures full of the deepest 

 interest, I will give you a description somewhat fully. 



The best way to obtain specimens is to take a 

 handful of weeds from any clear pond or ditch, and 

 place it in a glass vessel of water. After waiting 

 half an hour the hydrae will probably be seen in 

 various attitudes, some hanging loosely down, others 

 gracefully curving themselves upward and throwing 

 out tentacles many times longer than their bodies; 

 others shooting up their arms above their heads ; 

 others contracting themselves into mere jelly-like dabs ; 

 others attaching themselves by both extremities to the 

 side of the glass ; others floating on the surface of the 

 water, their-tail ends preserving them from sinking. 

 Their colours, too, may be nearly as various as their 



D 



