Chapter IX.— VARIATIONS IN STRUCTURE. 



Deformities in the .adult stages of the higher Crustacea center chiefly in the large 

 claws, which are more subject to mutilation than any other parts, owing to their 

 constant use as weapons. We will therefore consider first the variations in these 

 appendages. 



NORMAL VARIATIONS IN THE LARGE CLAWS. 



Aristotle (4) says of the claws of the lobster: ''In the Astaci alone it is a matter 

 of chance which claw is the larger, and this is in either sex." The difference between 

 the right and left claws is greatest in the small fiddler-crabs where, as in Gelasimus, 

 the large claw, according to Bate, can not reach the mouth, a power which it must 

 have originally possessed. 



It seems, as Aristotle remarked, a matter of chance whether the crushing-claw is 

 on the right or left side of the body; but this is not really the case. I have shown 

 that in Alpheus saulcyi, where the large crushing-chela can be recognized even before 

 the animal is hatched, the members of a brood are either right handed or left-handed, 

 that is, have the crushing-claw on the same side of the body. This seems to be a case 

 of direct inheritance from the parents, though not enough data were collected to settle 

 this point. (For a statement of the facts, so far as they are known, see 94, p. 376.) 



The large claw occurs about as frequently upon the right side of the body as upon 

 the left, without distinction of sex, as shown by the followiug table, embracing 2,433 

 individuals : 



Sex. 



Crushing 



claw on 



right side. 



Crushing 

 claw on 

 left side. 



Both claws 

 similar. 



562 

 602 



628 

 638 



1 



2 





Total 



1,164 



1,266 



3 





ABNORMAL VARIATIONS IN THE CLAWS. 

 SIMILAR CLAWS DEVELOPED ON BOTH SIDES OF THE BODY. 



A variation sometimes occurs in which the normal differentiation of the great 

 claws is wanting. Both claws are similar, developed either for cutting or crushing. 1 

 In examining over 2,400 lobsters, only 3 were found in which this abnormal variation 

 was present. It is, therefore, undoubtedly rare, and apparently has never been 

 previously described. Before examining these cases in detail it will be best to notice 

 the normal characteristics of the claws. This description is taken from a female — 

 length, 11 inches; weight, 24 ounces — with hard shell (compare fig. 20a, plate 15): 



Cmshing-claw : On right side; seven marginal spines on propodus, third spine 

 (from peripheral end) depressed; a small spine opposite the latter on upper side of 

 propodus. There is a small tubercle on the upper side of propodus, near articulation of 

 dactyl; in a corresponding situation below there are two tubercles, one considerably 



1 I have heard of a single case reported by a fisherman, where similar crushing-claws were 

 developed on both sides of the body. 



143 



