242 
bulletin op The bureau op pisheries. 
twisted rope-like mass is thu^formed, the forward strands of which are attached to the 
linkwork of hard tendons in the thorax. There are also in the thorax, rotator abdom- 
inis, ventral thoracico-abdominis and tergo-epimeral muscles, as well as flexors of the 
telson and tail fan in the abdomen. 
The weaker dorsal muscles (pi. xxxni) form a pair of segmented strands overlying the 
alimentary canal and dorsal blood vessel. They are inserted into the anterior border 
of each abdominal somite and diverge as extensor abdominis muscles in front, where 
they are attached to the walls of the thorax below the cervical groove. When the 
ventral muscles suddenly contract at the command of the nervous system, the combined 
pulls on successive joints bring the tail with expanded tail fan quickly and violently 
down upon the thorax, and the animal shoots backward through the water. By the 
contraction of the weaker extensor muscles the body is again brought into a horizontal 
position, and ready for another downward stroke. Raising the abdomen tends to send 
the animal forward, but owing to the obliquity and slowness of the stroke after closure 
of the tail fan the speed is but little checked. The muscular equipment of the great 
claws and legs are described in chapter vii. 
Two prominent light spots are conspicuous on either side of the carapace of an 
adult lobster, one at a point about an inch behind the base of the large “feelers,” and 
the other about as far behind the first, close to the irregular depression known as the 
cervical groove. (See p. 220.) The first, which is large and very conspicuous at the 
sixth stage, when the animal is barely five-eighths inch long, is the mark of a straight 
rod-like tendon which binds the carapace firmly to the internal skeleton below. The 
latter was without doubt originally a tendon-mark also, but in place of a distinct tendon, 
short muscle fibers issue from its margin, and from the groove in front, to be attached 
to the wall of the gill chamber. The sear-like impression conforming to the groove and 
immediately in front of it marks the attachment to the shell of the posterior suspensory 
muscles of the stomach sac. The powerful adductor of the jaws, by the contraction of 
which their cutting surfaces are brought to bear on the food, divides to give passage to 
this gastric muscle, one section of which is attached to the carapace in front of the 
groove, and the other just behind it on the endotergites, which as stated above are 
tendinous ingrowths from the fold itself. The anterior gastric muscles are inserted on 
the procephalic plates. 
Some fourteen pairs of extrinsic and intrinsic gastric muscles have been described 
by Williams (279) . These serve either to suspend the stomach sac to the inner wall of 
the carapace (anterior gastric, anterior dilators, and posterior and lateral gastrics) or to 
move its nicely articulated framework, bring the food to mill, work the grinding teeth, 
and to effect in some measure the sorting and straining of the comminuted food particles. 
THE BLOOD AND ORGANS OF CIRCULATION. 
The blood of the lobster when freshly drawn is quite colorless, leucocytes or white 
blood cells being the only corpuscles present, but after exposure to the air for a few 
minutes it becomes tinged with blue, and thickens or coagulates. The bluish color is 
imparted by a respiratory pigment called haemocyanin, which like the haemoglobin of 
