22 THE NATURAL HISTORY OF THE COMMON CRAYFISH 



be chelate. The two hindermost pairs, on the other 

 hand, end in simple claws. 



In front of these legs, come the great prehensile 

 limbs (10), which are chelate, like those which im- 

 mediately follow them, but vastly larger. They often 

 receive the special name of chelcB ; and the large terminal 

 joints are called the "hand." We shall escape confusion 

 if we call these limbs the forceps, and restrict the name 

 of chela to the two terminal joints. 



All the limbs hitherto mentioned subserve locomotion 

 and prehension in various degrees. The crayfish swims 

 by the help of its abdomen, and the hinder pairs of ab- 

 dominal limbs ; walks by means of the four hinder pairs 

 of thoracic limbs ; lays hold of anything to fix itself, or 

 to assist in climbing, by the two chelate anterior pairs of 

 these limbs, which are also employed in tearing the food 

 seized by the forceps and conveying it to the mouth ; 

 while it seizes its prey and defends itself with the forceps. 

 The part which each of these limbs plays is termed its 

 function, and it is said to be the organ of that function ; 

 so that all these limbs may be said to be organs of the 

 functions of locomotion, of offence and defence. 



In front of the forceps, there is a pair of limbs which 

 have a different character, and take a different direction 

 from any of the foregoing (9). These limbs, in fact, are 

 turned directly forwards, parallel with one another, and 

 with the middle line of the body. They are divided into 

 a number of joints, of which one of those near the base 



