AN EVENING AT THE MICROSCOPE. 189 



lowly Crustaceans is very similar in nature to the 

 substance called ckitine, which composes the outer 

 portions of insects. The head of Daphnia is not 

 covered by the shell, and the creature has but one 

 eye a bright, inquisitive-looking organ it is, too, 

 and apparently quite capable of doing duty for two. 

 There are very few males compared with the vast 

 number of the females. The contractile organ whose 

 working can easily be seen, acts as a kind of heart, 

 and there are five pairs of legs. The female pro- 

 duces two kinds of eggs. The " summer eggs," from 

 ten to fifty in number, are deposited in an open space 

 between the valves of the carapace, and are kept 

 there till the young are ready to be hatched ; but the 

 " winter eggs," which are only two in number, are 

 placed in what is called the saddle, on the back of 

 the carapace, where they remain till hatched by the 

 returning warmth of spring. 



The evening is wearing on, and we must not 

 permit ourselves any further diversion in watching 

 this frolicsome creature, for there is still another 

 tiny animal that I am anxious to prepare for the 

 inspection of my visitors, whose presence I had 

 already detected in a cursory and preliminary exam- 

 ination of the material with my pocket lens. This 

 is the Hydra. On one of the long white fibrils or 

 roots as they may be called, only they hang free in 

 the water of the duckweed in the aquarium I 

 observed a specimen of this most interesting group 

 of animals. To those accustomed to its appearance, 

 it can be detected even with the naked eye, for it 

 measures at least an eighth of an inch, quite a 



