HALF AN HOUR WITH CRUSTACEA. 233 



brachyura the " long-tailed " crustaceans, as the 

 lobsters, and " short-tailed," as the crabs. In the 

 latter, the great broad shield covering the head, &c., 

 is termed the carapaee, the so-called tail being in 

 reality the abdomen. In the crabs, this is reduced 

 to a mere rudiment, and is always tucked under the 

 carapace, the vulgar name for it being the " apron." 

 Although the twenty-one segments of the body of 

 a crustacean are modified in such a singular manner, 

 they are never wholly lost sight of. Even when 

 they are fused together, they can be told by the 

 pairs of appendages. We have already spoken of 

 the mouth as having no real jaws, but modified feet. 

 The hinder pair of the mouth appendages are so 

 little altered in appearance as to be called " foot- 

 jaws." The first three pairs of legs placed under 

 the carapace are usually armed with nippers the 

 organs placed under the abdomen, or tail, being 

 termed " swimmerets," because these are used, like 

 the boards of a paddle-wheel, in moving about in 

 the water. The mouth of a crab or lobster opens 

 into a globular stomach, which is furnished with a 

 calcareous apparatus for triturating food. The 

 heart is placed along the back, and is therefore 

 called dorsal; the nervous system being arranged 

 beneath, or in the ventral part of the body. Perhaps 

 the most wonderful arrangement in the structural 

 economy of the Crustacea is in their mode of 

 breathing. If you examine a tolerably large lobster, 

 you will find that beneath the broad carapace the 



