410 THE INVERTEBRATA 



maxillipedal somites are fused into a triangular mass. In front of the 

 mouth the plate known as the epistorne represents the mandibular and 

 antennal sterna. From this a ridge extends to the median rostral 

 tooth, separating two sockets in which stand the antennules. A down- 

 ward process from the front, abutting on the basal joint of the antenna, 

 separates each of these sockets from the orbit of its side. The two- 

 jointed eyestalk arises close to the median line and passes through a 

 gap between the frontal process and the antennal base to enlarge 

 within the orbit. 



The abdomen is reduced to a flap, turned forwards and closely ap- 

 plied to the sterna of the thorax. Its ventral (upper) cuticle is thin. 

 It is broader in the female than in the male, in which its 3rd to 5th 

 somites are fused. Two small knobs on the 5th thoracic sternum, 

 fitting into sockets on the 6th somite of the abdomen, lock the two 

 together as by a press button. 



The antcnjmles have short flagella and can fold back into the sockets 

 mentioned above. The antennae also have a short flagellum. They have 

 no exopodite (scale) and their coxopodite is represented by a small 

 operculum over the opening of the antennary ("green") gland. The 

 month parts are shown in Fig. 288 . In the mandibles, the biting edge 

 (incisor process) is toothless and the molar process reduced to a low 

 mound behind the biting edge. The palp is stout and the first two of 

 its three joints are united. The maxillules and maxillae have the usual 

 endites well developed. The scaphognathite of the maxilla is shaped 

 to fit the exhalant passage of the gill chamber. The maxillipeds have 

 epipodites produced into long, narrow mastigobranchs, fringed with 

 bristles which brush the gills. The flagella of their exopodites are 

 turned inwards and the endopodite of the first of them is expanded 

 at the end and helps to border the exhalant opening for the respiratory 

 current. The third pair are broad and enclose the mouth area from 

 below. The legs lack an exopodite and have the usual joints (p. 336) 

 in the stout endopodite, but the basipodite and ischiopodite are 

 united. The first leg has a strong chela: concerning the physiology of 

 its muscles something is said on pp. 138, 142. The others differ from 

 those of the crayfish chiefly in that none of them are chelate. The 

 animal, as is well known, walks sideways with them. Abdominal limbs 

 are present in the female only on the 2nd to 5th somites. On a short, 

 one-jointed protopodite they bear two long, equal, simple rami, covered 

 with setae to which, as in other decapods, the eggs are attached by a 

 covering secreted by dermal glands. In the male, the abdomen bears 

 limbs only on its first two somites, and they are uniramous and adapted 

 for transferring the sperm, the endopodite of the second working as 

 a piston in a tube formed by that of the first. 



In feeding the food is seized by the chelae, which place it between 



