The growth of the animal is effected by moulting. The /Crustacea/ are named from the crust-like covering which envelops them. It is a horny material, called chitin, in which are deposited particles of carbonate of lime, making a rigid envelop which would prevent all freedom of motion, were it not that there are spaces free from lime, and thus flexible joints are left. When the animal expands it throws off this hard covering and secretes a new and larger one. As the time of moulting approaches, the old covering becomes loosened, and a delicate new one is formed beneath it. The old shell splits open across the back just behind the carapace, and the soft animal withdraws first its cephalothorax and then its abdomen, leaving the cover complete, including even the covering of the eyes and the lining of the stomach. The [pg249] 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 accidents, 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 comparatively 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=