NATURAL HISTORY OF AMERICAN LOBSTER. 
265 
dactyl and afford a surface for the attachment of the huge flexor and smaller extensor 
muscles. Each tendon is a keeled plate which is developed in a flattened pocket of the 
skin, but the closing muscle of the great claw being the largest and the strongest in the 
body requires the la>rgest tendons. The tendon of the flexor (L /?.®) is a broad leaf- 
shaped plate, keeled above and below, while that of the weaker opening muscle is narrow 
and strap-shaped. 
At the time of molt these huge tendons, like all others in the body, are drawn out, 
attached to the cast-off shell, and leave deep open poekets into which in a large animal 
the little finger can be easily inserted. As soon, however, as the soft claw becomes 
tense with blood, the water is driven out and, the opposed surfaces of the pocket uniting, 
a new tendon is gradually formed. (Compare fig. 1, t p, pi. XLiii.) 
The coarser flesh of the elaws represents, as we have indicated, the eharaeteristic 
flexor and extensor museles, while the ‘ ‘ fine meat ’ ’ of the daetyl (fig. 3 , pi. xlvi) and distal 
half of the propodus is eomposed of a sponge work of involuntary muscle fibers in addition 
to fine-blood vessels of the arterial system, nerves, glands, and eonnective tissue, the 
whole being enveloped by the soft pigmented skin (pi. xl). No special sense organs, 
aside from the setae, have been deteeted in it. The meshes of the sponge work form 
a system of communicating sinuses into which the arteries appear to open through very 
small branches or capillaries. 
During the molting process, when the fleshy mass of the claw is drawn through a 
series of narrow rings as if it were a pieee of eandy, the blood is of necessity withdrawn 
from these parts. The sponge work is an adjustment which meets this prime need of the 
molting period. At the time of molt the museles are extremely tense and the flesh hard, 
and the contraction of the fibrous sponge work apparently keeps back the flow of blood 
until the animal escapes from its old shell, when it again becomes completely relaxed 
(see P-206). 
The abundant blood always found in the large elaws, except when molting, is supplied 
by a large artery, whieh at the point of entry from the fifth segment divides into an inner 
and a smaller outer braneh. The inner division passes between the two museles, and 
gives off small twigs in. its course; then as it eurVes outward over the distal end of the 
flexor muscle, it sends off somewhat irregularly a branch to the upper and lower division 
of eaeh muscle, and to upper and lower parts of dactyl and propodus. 
The nerves of the great eheliped (pi. xl) consist of two main bundles (n* and n?), 
made up of a number of closely related strands. In the basal segments of the limb the 
larger and more complex bundle (ra^) is anterior while the smaller bundle (rd), which is 
double, follows it closely on its posterior or outer side. 
The nerves usually enter the elaw in three closely related strands, one of whieh. sup- 
plies ehiefly the extensor, one the dactyl and flexor, while the outermost branch is dis- 
tributed to the flexor and large “finger” of the claw. Both arteries and nerves regularly 
divide and subdivide in the terminal parts of the elaw to form a very eomplicated 
system. 
