36 Animal Life by the Sea-shore. 



IV.— CRUSTACEANS AND OTHER 

 ARTHROPODS. 



The Crustaceans form a subdivision oi an enormous group oi 

 invertebrate animals known as the Arthropods (jointed-hmbed), 

 whicli indudes, besides the Arachnids (Spiders, Scorpions, 

 Tides, etc.), the M^'riopods (Centipedes and Millipedes) and the 

 Insects. In their t3rpical form they may be distinguished from 

 the other Arthropods by the ]n-esence of two pairs of antennae 

 or feelers on the front part of the head, and also by the larger 

 number, combined with great diversity in structure, of the 

 limb-like appendages carried bj? the jointed body. The majority 

 of Crustaceans breathe by gills, which are generally developed 

 from the appendages ; many of the lower forms are devoid 

 of special organs for this function. After the Insects, the 

 Crustaceans probably constitute the largest of all classes of 

 animals, and, although mainly marine, they ha\'e representatives 

 in almost every possible situation, in fresh waters, and even on 

 land. The most familiar forms are naturally such as find place 

 on the fishmonger's slab ; the lobster, crawfish, prawns, shrimps 

 and crabs are excellent examples of what are known as the higher 

 Crustaceans. A rapid inspection will show that these types 

 agree in man}/ important characters, the body being divided 

 into a large firm carapace bearing a pair of stalked eyes anteriorly, 

 and a jointed abdomen, popularly but quite erroneously regarded 

 as the tail, consisting of six rings or segments and ending in a 

 flat piece or telson, the true tail. Both the carapace and the 

 abdomen bear limb-like appendages modified to subserve 

 almost every purpose. The first two pairs are antennae or 

 feelers, situated to the front of the carapace ; on the lower 

 surface, surrounding the mouth, there are six pairs set close 

 together and acting as ja\\'s, while the posterior part of the 

 carapace bears five pairs of long walking-legs, some of which 

 may form pincers at their extremities. The rings of the abdomen 

 are provided with swimmerets, two-raj'ed appendages used in 

 swimming. The five pairs of walking-legs are bj' far the most 

 conspicuous of these appendages, and for this reason the name 

 Decapoda has been bestowed on this cUvision of the higher 

 Crustaceans. E\'en the most superficial observer will notice 



