212 POPULAR HISTORY OP THE AQUARIUM. 



may have five or seven pairs of legs. All the legs, joints of 

 the tail, bod}^, and head, are covered by a horny or shelly 

 crustj from which their name is derived, and Avhich causes 

 them to be placed, in commercial and domestic classification, 

 with scallops, cockles, oysters, and periwinkles, under the 

 general appellation of " Shell-fish" 



The "Stalk-eyed Crustacea," or those which have the 

 eyes placed on a movable pedestal, include those familiarly 

 known as table articles, and worthily represented by the 

 common eatable Lohstei-, the great eatable Crah, and the 

 brown market Shrimp^ or more luxuriant Praivn. Re- 

 serving the Eutornostraca for another Chapter, let us apply 

 our observations to the above representatives and their 

 constituents. ' 



Professor Bell has well explained the construction of these 

 animals in the Introduction to his ' History of Stalk-eyed 

 Crustacea.' The body of a crustacean is jointed, or com- 

 posed of segments or rings, with appendages or limbs at- 

 tached to each. " The true normal number of segments," 

 remarks the Professor, " taking the whole class, appears to 

 be twenty-one, of which, according to oar present know- 

 ledge, seven must be considered as belonging to the head, 

 and an equal number respectively to the thorax and the 



