CRUSTACEANS 249 



new shell is rapidly hardened, being already formed when the old 

 one is cast, and the animal regains its normal condition in about 

 a week ; in the meantime it is defenseless, and lies quiet in some 

 secluded place. -Moulting is an exhausting process, and is attended 

 with great dangers. A great mortality occurs at this time from ac- 

 cidents, from weakness, and also from helplessness in case of attack. 

 The hair-like processes scattered over the shell, often like 

 fringes, are said to be organs of feeling. 



SUBCLASS ENTOMOSTRACA 



These are Crustacea of small, often microscopic size, of com- 

 paratively simple organization, and with appendages adapted 

 to serve the purpose of respiration. These minute animals 

 may be obtained by skimming the surface of the water with 

 a muslin net, preferably at night, then washing off the inside of 

 the net with a small quantity of water into a glass dish. Place the 

 dish on a dark surface before a light, and the little creatures will 

 gather toward the light, and may be satisfactorily observed with 

 a glass. 



ORDER COPEPODA 



This order, though composed of minute forms, is one of great 

 economic importance, from the fact that the little crustaceans exist 

 in vast numbers and furnish a very considerable part of the food 

 of many fishes. Cyclops is the most common of the fresh- 

 water, and Cetochil^ of the marine genera. These, together with 

 other genera, swarm in water wherever life exists, from the smallest 

 pools and ditches to the broad surface of the ocean. Without hav- 

 ing drawn a surface-net on some sheltered bay, it is difficult to have 

 an idea of the myriads of Entomostraca in the sea. Although 

 nearly transparent and of such delicate texture as to be almost 

 jelly-like, they sometimes color the sea with a reddish tint for 

 miles. Whales which have baleen, or fringes of whalebone, 

 in the mouth subsist on. these small organisms, which are 

 called " brit " by the whalemen. The whales, sometimes in schools, 

 rush through the water with open mouths, engulfing these little 



