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 Cetochilus 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 Hntomostraca 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 
