THE CRUSTACEA 



have a small palp. In the Tanaidae the whole appendage is vestigial. 

 The lower Up of the Apseudidae (Fig. 117, A) is peculiar in having 

 each of the lobes terminating in a movably articulated lappet. 



The first pair of thoracic appendages are muxillipeds (Fig. 117, D), 

 agreeing with those of the Cumacea and Isopoda in having coupling- 

 hooks on the endite of the basipodite. The epipodite (ep) projecting 

 backwards into the branchial chamber is most fully developed in the 

 Apseudidae, where it consists of a peduncle bearing a spoon-shaped 

 membranous plate which terminates posteriorly in a filiform pro- 

 cess and is produced anteriorly as a rounded lappet fringed with 

 setae. The resemblance of this apparatus to the branchial 

 epipodite of the Cumacea is unmistakable, and the filiform 

 termination may be compared with the inflected apex generally 

 found in that group. A small lobule found in some Tanaidae may 

 perhaps represent the exopodite. In the Tanaidae the maxillipeds 



— en. 



Pig. lir. 



Mouth-parts of Apseudes spinosus. A, lower lip with movable lobes. B, maxillula ; p, palp. 

 C, maxilla. . D, maxilliped ; en, terminal lobe or endite of basipodite ; ep, ejiipodite. (After 

 Sars.) 



are more or less united at the base, the coxopodites, and some- 

 times also (as in the Amphipoda) the basijDodites, being coalesced. 



The second pair of thoracic limbs are in nearly all cases com- 

 pletely chelate and are usually much stronger than the succeeding 

 pairs. The third pair in the Apseudidae are flattened and apparently 

 fossorial in function. The minute exopodites (Fig. 116, ex) with 

 which these two pairs are provided in many Apseudidae are placed 

 close to the exhalent and inhalent oj^enings of the branchial cavity 

 respectively, and by their vibratory motion assist in producing the 

 respiratory current. In all the thoracic limbs the coxopodite is 

 very small, and in the posterior five or six pairs the limb ends 

 in a curved claw. 



In the Apseudidae there are five pairs of oosfegites (the first 

 pair very small) attached to the thoracic limbs, from the second to 

 the sixth pair. In some, perhaps all, Tanaidae only one pair of 

 oostegites is present, on the sixth thoracic limbs. 



The pleopods may be fully developed in both sexes, but some- 

 times they are reduced in number or altogether absent in the 



