Chapter VII.— THE GREAT FORCEPS OR BIG CLAWS. 



THE CRUSTACEAN CLAW. 



The last ten thoracic legs of higher Crustacea all end in hard-pointed segments 

 technically known as dactyls. In the account which follows, when not thus desig- 

 nated, they will be called "single claws," "nails," or "digits," the original meaning of 

 the word. In Palinurus, the spiny lobster, all of the thoracic legs end in talon-Uke 

 claws of this simple type; but in the true lobsters, crayfishes, crabs, and many other 

 decapods a unique organ is developed in certain of the forward legs by the extension of 

 an opposable finger-like process of the subterminal segment, the propodus, which is 

 often large and powerful. In the great cheliped of the lobster (pi. xxxiii and xxxvii) 

 this division is also called "the hand" and the terminal part of it the "index," as dis- 

 tinguished from the opposed "thumb" or dactyl. Thus is formed the admirable 

 forceps, commonly known as the "claw" or chela.'' 



Those legs ending in forceps are described as chelate and the others as nonchelate, 

 and the technical use of these terms is unobjectional. This, however, need not lead to 

 the ambiguity of sa5dng that the last two pairs of legs in a lobster or crayfish have no 

 "claws." To avoid this absurdity, we may adopt Huxley's terms, " double claws " and 

 "single claws" for the forceps of the first three and the nails of the last two pairs of 

 legs, respectively, since they describe the conditions met with in both lobsters and cray- 

 fish exactly. The chelate legs all pass through the simple claw stage in either the egg or 

 early larval state. 



The big claws of the lobster are remarkable organs whether considered in the light 

 of their structure, their development, or the process of their renewal, and. the more we 

 study them the more remarkable they appear. 



In most of the higher Crustacea the great claws are the chief weapons for both 

 attack and defense and very efficient means for seizing and rending the prey, as well 

 as for grasping and holding the female in the act of pairing, when the spermatophores 

 are transferred to her seminal receptacle or to some other part of her body. 



While three pairs of pereiopods in this animal bear double claws or forceps, in the 

 first pair alone are they entitled to be called "great.'' In many crabs, as well as in 

 the lobsters and crayfish, the great claws are weapons whose grip is not to be despised. 



In some of the crajrfishes the great chelipeds are equal to about one-quarter of the 

 weight of the entire animal, while in lobsters above medium size their proportionate 

 weight sometimes reaches one-half, and tends to increase with age. Moreover, the 

 disproportion between the big claws of either side, which are normally asymmetrical, 



a Latinized from the Greek *ord for any armed appendage; in plural form chelae, corrupted from chele. 



253 



