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 

 aegree, 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. i, 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 setje 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, fd 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. 



