CHAPTER VII 



THE CRUSTACEA 



IF we look at a lobster, a scorpion, a centipede, a caterpillar, 

 and a beetle, we shall see that they have in common certain well- 

 marked features. They all possess a hard or tough integument ; 

 the body is more or less distinctly divided into segments ; the 

 legs, feelers or antennae, mouth parts, etc., are also divided by 

 joints into a number of segments, and are covered with the same 

 hard or tough coat as the body ; while certain characteristic points 

 in the arrangement and structure of the internal organs are common 

 to all. For this reason these animals so diverse in form and habit 

 are included in one comprehensive group or phylum, called the 

 Arthropoda, and divided into four great classes : (i) the Crustacea ; 

 (2) the Arachnida (spiders and scorpions) ; (3) the Myriapoda 

 (centipedes and millipedes) ; and (4) the Insecta (butterflies, moths, 

 beetles, flies, etc.). 



The class Crustacea comprises the Lobsters, Crabs, Crayfish, 

 Shrimps, Prawns, Sandhoppers, Water-fleas, Barnacles, and Wood- 

 lice, besides a host, of chiefly small related forms that have no 

 popular names, and are practically only familiar to the specialist. 

 The class contains a vast assemblage of animals most diverse in 

 size and appearance, and mostly aquatic in their habits. They are 

 an interesting group of animals, and many of them pass through 

 a remarkable series of transformations or metamorphoses ere 

 reaching the adult stage. 



If a Shrimp or a Lobster be examined, it will readily be noticed 

 that its hard body-covering or integument is made up of a number 

 of segments jointed together, to which are united by jointed 

 sockets the claws, legs, and long feelers or antennae. To give 

 greater protection to the soft parts of the body, a number of these 

 segments are soldered together so as to form one piece ; but these 

 fused body-rings can always be detected, for normally each seg- 



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