CRUSTACEANS. 155 



The articulated appendages situated beneath the tail are so 

 rudimentary that they are no longer recognizable as instruments 

 of progression, and it is at once evident, when we examine the 

 manner in which these creatures use their tails in swimming, that 

 any large limbs in this position would materially impede the 

 movements of animals presenting such a construction. The false 

 feet, as these organs are called, are merely available as a means of 

 fixing the eggs which the female lobster attaches to them. 



The tail is the great agent of locomotion, and for this purpose 

 it is terminated by a fin formed of broad plates, so arranged that, 

 while they will close together during the extension of the tail, 

 and thus present the least possible surface to the water, they are 

 brought out to their full expansion by its down-stroke ; and such 

 is the impulse thus given, that a lobster will dart backwards to a 

 distance of twenty or thirty feet by one sweep of this remarkable 

 locomotive instrument. 



The Crustacea are divided into several important sections, each 

 of which will require separate notice. 



TEN-FOOTED CRUSTACEANS. ORDER DECAPODA. 



The first great division of this extensive class has received the 

 name of Decapoda* (ten legs], from the circumstance that their 

 locomotive limbs are always ten in number. 



The Decapods are divided into three groups, known by the 

 somewhat unpronounceable names of Macroura, Brachyura, 

 and Anomoura ; when translated into English, however, these 

 formidable-looking words simply mean Big-tails > Little-tails, and 

 Queer-tails. 



The division Macrouraf (big-tails, includes the Lobsters, 

 Cray-fishes^ Shrimps, and Prawns. 



The Sea Cray-Fishes (Palinurus) have their antennas very large and 

 studded with sharp spines ; their shell is likewise rough, covered with prickles, 

 and armed in front with strong spiny protuberances. They seldom frequent 

 any but rocky or stony places, live there on fish and divers marine animals, 

 and attain, after some years, to the length of a foot, measured from the head 

 to the extremity of the tail. In some places, little favourable to fishing, these 

 Crustaceans, being less exposed and more tranquil, may live a very long time 

 and acquire a large size: some have been obtained nearly three feet long. 

 They are caught in wicker baskets, baited with flesh, much in the same way 

 as lobsters. 



* 5fKa, deca, ten; irovs, Trodos, pous, podos, a foot. 

 f ,ua/cpos, macros, long ; ovpa, oura, a tail. 



