CRUSTACEA. ?3 



very sensibly, though at first it may not be seen, con- 

 cealed as it is by the short hairs upon its apex and 

 the longer hairs on either side. Passing to the third 

 and second pairs of walking-legs, the scholars will be 

 able to infer from their own observations thai the 

 counterpart of this little spine, in each pair, is the jaw- 

 like prolongation of the sixth section ( r). equal in 

 length to the last section. This growth has taken place 

 on the inner side, and the result is the formation of a 

 clasping organ, of which one section is movable while 

 the other is immovable. Here. then, whenever the 

 animal requires it, the movable part will begin to clamp 

 objects against the immovable portion : or. in other 

 words, rudimentary jaws will be formed, which need 

 only teeth to become capturing or crushing organs 

 like those at the ends of the first pair. These walking- 

 legs are carried well forward under the first pair, and 

 are useful in lifting up, supporting, and moving these 

 heavy parts. 



The movable section of the jaws alone is used when 

 the animal is walking upon a hard surface, and then it 

 has the same function as die corresponding seventh 

 section in the fourth limb. The worn, white tip shows 

 again just where wear takes place. The nipping power 

 of these jaws is slight, but they are used to lay hold of 

 objects when the animal is in danger of being dragged 

 out of its hole under the rocks, or from between masses 

 of sea-weed, and are also particularly useful when some 

 fish, or other large prey, struggling to get free, drags 

 it along over open ground. The jaws are then widely 

 opened, and forced dee]) into the sand, and. together 

 with the other legs, afford a very firm resistance. 



