228 
bulletin of the bureau of fisheries. 
cervical groove, and between two white tendon marks; when they work the “doors” are 
swung to with force. 
The masticatory surface of each jaw is represented by the short side of the triangle 
which meets its fellow on the midline in front of the labrum. It is divided by a deep 
groove into an outer cutting ridge, capped with a dense mass of yellow chitin, and a 
lower and flatter surface, which appears to be available for mastication in but a slight 
degree, if at all. The groove (g, fig. 7, pi. xxxv) not only protects the fleshy upper lip, 
but gives play to a 3-jointed hairy palp, the two distal segments of which are sup- 
posed to represent the endopodite. The palp is actuated by muscles lodged in the body 
of the mandible itself, and possibly serves to direct food particles to the mouth, below 
the level of the groove, and just beneath the tip of the labrum. 
The lobster’s mandibles work essentially on the principle of the modern stone- 
crushing machine; little or no lateral motion being possible in an animal with a hard 
shell, they can serve only by repeated closing movements to divide and triturate the 
larger particles of food, which, having resisted the preceding mouth parts, get pinched 
between the meeting edges of the swinging “doors.” 
The leaf-like first pair of maxillae, the smallest of the mouth parts (fig. 1, pi. xxxvi), 
bear on their first segment a fringe of stiff hairs and on their second a comb of bristles, 
which help to pass up the food or mince it when soft. The second maxilla serves chiefly 
as a “bailer,” or rather as a fan for driving water out of the respiratory cavity in front. 
(Fig. 2, pi. xxxvi.) This thin elastic plate lies nearly horizontal, the divided protopodite 
and rudimentary endopodite closely fitting over the mandible and the conforming first 
maxilla, and is formed by the fusion of an anterior exopodite and posterior epipodite, 
the upper side of the former and lower side of the latter, when not in rythmic move- 
ment, resting against the sides of the respiratory cavity. (For action of fan see p. 
247.) The “masticatory ridges,” or setigerous coxa, and basis of the second maxilla 
are partially cleft and distinctly separated by a superficial fold. 
The first pair of maxillipeds (fig. 3, pi. xxxvi), except for one or two particulars, are 
modified only in minor details from the condition seen in the first larva. The parts are all 
rather soft, flattened, and curved to fit over the swelling mandibles and one another; the 
setae of the meeting borders of the bases and coxae are soft and useless for mastication; 
the exopodite lies against a shallow groove on the outer side of the two-jointed endo- 
podite, the groove being marked by independent rows of setae and the branch pre- 
senting a modified four-sided appearance. There is a long respiratory epipodite which 
carries no gill, but a part of its outer border is folded or turned under so as to form 
a trough, Jd in which plays the posterior blade of the “bailer,” or scaphognathite. 
In the slender, outwardly swelling second maxilliped (fig. 4, pi. xxxvi) there is a 
fused joint ( x ) between the ischium and reduced basis. The brushes of setae which fringe 
the inner border of this compound segment and the long curved meros are all soft, 
and on the small knob of the dactyl only do we find short stiff spines which can in any 
way effectively react on the food in mastication. Both epipodite and podobranchia 
are rudimentary. 
