CRUSTACEA 



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Class I. CRUSTACEA Fresh-water Crustacea. 



The smallest are to be found in the water from any stagnant pond or pool. 

 If a bottle of such water be examined closely, you are sure to see a number 

 of minute creatures darting and jerking about in all directions. These are 

 Water-fleas and Cyclops, in size less than of an inch, which, to examine 

 thoroughly, should be watched through your microscope (the home-made 

 apparatus described elsewhere in this book will serve excellently for this 

 purpose). 



i. The Water-flea (Daphnia pulex) is not to be confused with the House- 

 flea, the latter being a real insect. It is recognized by its oval shape and its 



Crustaceans, i. Cyclops, the one-eyed crustacean, i (a). Young cyclops. 2. Water-flea. 

 2 (a). Egg-bag of water-flea. 3. Cypris. 4. Asellus aquaticus. 



prominent beak. Under the microscope its shell (or carapace) is so transparent 

 that you may watch its inner organs working, its heart beating, and its eggs 

 in situ. The male is very rare. The female produces two kinds of eggs 

 winter and summer. The former remain inside the carapace, which is shed 

 by the female in due time and drops to the mud, where the eggs are thus 

 protected till the spring. They may freeze, or the pond may dry up, but yet 

 they survive. Indeed, the carapace may be blown by the wind far from 

 its original resting-place and find a home in a new pond. This accounts 

 for the presence of these creatures in practically every piece of water in the 

 country. The summer eggs are laid when food is plentiful, and they hatch 



