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 
greater and greater degree of torsion, and 
finally extending through so great an arc, 
although it is conceivable that such a 
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- 
gard this torsion of the crustacean limb as 
the resultant effect of use through inher- 
itance. The carpal podomere has but 
one flexor and one extensor muscle, both 
of which react on the claw at points out- 
side of the joint itself; at the same time 
the muscles, of course, pull on the shell 
of this part at their points of origin, but 
no conceivable position or strain of these 
fibers can convert the pull into a twist. 
If the increasing weight of the claws in 
the growing animal had any effect upon 
their ultimate position it should tend to 
turn them outward. In other words, their 
modification is just the reverse of what 
we should expect were the effects of 
strain or use inherited. 
If we examine other crustaceans we 
find that the big claws open inward, up- 
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 ( Gclasimus 
pugnax ) they incline inward, 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 ( Carcinus , Callinectes) the claws 
open obliquely outward. It therefore appears that in the rotation of the crustacean 
Fig. 6 and 7. — Great first and small left third claw feet of adult 
lobster with pins (mo. 2-7) inserted in the axes of articulation 
of successive podomeres, to indicate normal torsion in the great 
cheliped. Position of the big claw up to the fourth stage is iden- 
tical with that of the little claw of the slender leg. Compare 
plates xx vm and xxxi, with figure 14 of text. Cp carpus; D, 
dactyl, and X, breaking joint. Podomeres or segments oi per- 
manent limb numbered, as in all succeeding figures, in Arabic 
numerals, from base to apex. 
