264 
bulletin 0 E the bureau of fisheries. 
The toothed claw, as already remarked, is richly supplied with tufts of sensory hairs 
above and below the line of teeth and also along the margin of the claw near its tip. 
These are specially abundant on the underside, and with them the animal is constantly 
feeling the bottom when it assumes the common alert attitude with the tips of the claws 
bent down. These tactile setse are arranged in bundles of 200 to 300 or more short, stiff 
bristles which, like little scrub- 
bing brushes, project from de- 
pressions in the shell. The 
floor of each depression is a 
sieve plate, the perforations of 
which correspond to the num- 
ber of setse as well as to the 
number of nerve fibers supply- 
ing the bundle. In the adoles- 
cent stage, when the lobster has 
attained a length of 3 or 4 
inches, the setse of the lock forceps become large matted tufts which sometimes com- 
pletely conceal the teeth. (Compare fig. 15 and 16). 
THE CRACKER OR CRUSHING CLAW. 
In place of tooth-like spines the great crushing claw presents a number of rounded 
tubercles, both large and small, single or double, and arranged in a characteristic manner 
(fig. 2 and 3, pi. xliii). These crushing tubercles are very dense, and in old hard-shell 
Fig. 13. — Large segment of right toothed claw from above, to show the periodic teeth; compare 
projection in figure 12; u h ( ridge ), upper ridge of sliding lock joint. 
lobsters the pigment and enamel is completely worn away from long and rough usage. 
The tips overlap slightly, but the dactyl is curved, and not straight as in the toothed 
claw, consequently when closed there is often a wide gap between the jaws, the tubercles 
touching at but one or two points only. (Fig. 2, pi. xxxvn.) 
The crushing claw, as shown in the drawing (pi. xl), has a far more powerful muscu- 
lature than its fellow, and is accordingly richer in its supply of blood vessels and nerves. 
Two tendons (fig. 2, pi. xli) spring from opposite sides of the proximal end of the free 
Sp 
V A 
S’ 
O' 
IV 
in 
n 
I 
Fig. 12. — Projection of serial teeth in segment of big claw of large adult lobster 
represented in figure 13, showing alignment to lower or ventral ( v ), originally the 
anterior, side, the position of the tip, spur (Sp), and the large displaced lock 
spine (L), the two last serving as guide posts for identification of the periods 
i-iv. In this and following figures the periods are enumerated from the distal 
to the proximal end of the claw. 
