258 BULLETIN OF THE BUREAU OF FISHERIES. 



their under sides. This rotation is completely effected at the fourth stage (pi. xxxi) 

 and with the molt which registers so many other marked changes in the structure and 

 habits of this animal. It is responsible for the torsion or twist to be clearly seen in the 

 carpus of the limb. In conformity with this change in position, the claw has undergone 

 a change in coloring, for the deep green chromogen pigments which cover the present 

 upper surfaces are completely lacking from their pale red under sides. 



It would appear in the highest degree improbable that this condition in the big claws 



could have been produced through the in- 

 heritance of slight variations leading to a 

 g / I greater and greater degree of torsion, and 



finally extending through so great an arc, 

 '^ although it is conceivable that such a 



p /_ AV^^-" 7 variation may have been correlated with 



others which were of so favorable a char- 

 acter as to be of selective value and to 

 have been "dragged" along with them. 

 Again, it is even more difficult to re- 

 6 gard this torsion of the crustacean limb as 



n...J. //] \^ \- Cp the resultant effect of use through inher- 



itance. The carpal podomere has but 



7'"' / / '^''^ » ^^ 5 one flexor and one extensor muscle, both 



■" ^^^vl_^rTy of which react on the claw at points out- 



- K"^ ^J- -^1 >v -'' ^^^^ °^ ^^^ joint itself; at the same time 



-Cp ^v) ■•^'^v»*--2 ^^^ muscles, of course, pull on the shell 



of this part at their points of origin, but 

 no conceivable position or strain of these 



S—-z^^^ \ ^ -J M,- 4 fibers can convert the pull into a twist. 



• 2 If the increasing weight of the claws in 



the growing animal had any effect upon 



- 5 their ultimate position it should tend to 



^ ,!,,,.,, , turn them outward. In other words, their 



Fig. 6 and 7. — Great first and small left third claw feet of adult 



lobster with pins (no. 2-7) inserted in the axes of articulation modification IS jUSt the revCrSC of what 



of successive podomeres, to indicate normal torsion in the great -y^g should CXOect Were the cffcCtS of 

 cheUped. Positionofthebigdawuptothefourthstageisiden- . * i_ • j 



tical with that of the htUe claw of the slender leg. Compare Strain or USC inherited. 



plates xxvni and XXXI, with figure 14 of text. Cp carpus; D. jf ^g examine other crustaceaus we 



dactyl, and X, breaking joint. Podomeres or segments oi pei^ 



manent limb numbered, as in all succeeding figures, in Arabic find that the big clawS OpCU iuward, Up- 



numeiais. from base to apex. Ward, or outward, irrespective of their 



relative size or weight. In the Alphei, which usually have one claw of enormous size 

 and of peculiar structure, the dactyls open outward, while in the fiddler crabs {Gelasimus 

 pugnax) they incline invmrd, as in the lobster. This is true not only of the single huge 

 claw of the male fiddler but of its diminutive fellow and of the small, almost rudi- 

 mentary chela of the female. In the common crabs {Carcirms, Callinectes) the claws 

 open obliquely outward. It therefore appears that in the rotation of the crustacean 



