368 THE INVERTEBRATA 



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 antennules 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 

 mouth parts are shown in Fig. 274. 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. 300) 

 in the stout endopodite, but the basipodite and ischiopodite are 

 united. The first leg has a strong chela. 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 for the attachment of the eggs. 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 second. 



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

 the mandibles. These do not chew it, but, unless it be soft enough for 

 them to sever a morsel when they close upon it, they hold it while the 

 morsel is severed by the action of the hinder mouth limbs. The 

 basal endites of the maxillules, the mandibular palps, and the pointed 

 lab rum push the food into the mouth. The alimentary canal resembles 

 in general features that of the crayfish. Its mid gut is short, and bears 

 a pair of long dorsal coeca which end, each in a coil, at the sides of the 

 cardiac division of the proventriculus or "stomach". The hind gut, 

 just before entering the abdomen, gives off dorsally a long tube coiled 

 into a compact mass. The "liver" is large and enters the carapace 

 fold. In the antennal glands the whitish medullary portion found in 



