246 



THE CRUSTACEA 



the exopodite. The maxillae (Fig. 140, C) generally consist of 

 four segments ; the second and third have each two endites and 

 the third a slightly developed flabelliform exite (exopodite) ; the 

 fourth segment generally forms the palp, but in Bentheupliausia the 

 palp consists of three segments. 



None of the thoracic limbs (Fig. 141) are specialised as maxilli- 

 peds, the first pair being similar in general structure to the 

 succeeding pairs. The coxopodite is distinct and of considerable 

 size ; the main flexure of the limb is between the meropodite and 

 carpopodite ; the terminal segment is blunt and is without a 

 distinct claw, bearing, as a rule, only a group of setae and 



br.~ 



Fio. 141. 



Thoracic appendages of Meganyctiphanes norvegica : A, first ; B, second ; C, seventh ; D, 

 eighth, br, branchia (epipodite) ; en, endopodite ; ex, exopodite ; p, luminous organ. 



spines ; the exopodite is flattened and fringed with long natatory 

 setae. 



On the outer side of the coxopodite is attached an epipodite (br), 

 which is small and simple in form on the first pair, but ramified in 

 a complex fashion on the other pairs of thoracic limbs. These 

 branchiae, which are apparently quite homologous with the podo- 

 branchiae of Decapoda, are not covered by the carapace, but hang 

 out freely at the sides of the body. 



The last pair or the last two pairs of thoracic appendages are 

 commonly much reduced or quite vestigial, though the branchiae 

 connected with them are of large size (Fig. 141, D). The coxopodite 

 of the first pair is usually slightly produced inwards, but only in 

 Bentheupliausia does this so-called "masticatory lobe" differ very 

 perceptibly from that of the succeeding pairs. A more important 

 exception to the uniformity of the thoracic limbs is found in the 

 genera forming the sub-family Nematoscelinae. In these, one of 

 the pairs, the second or the third, has the endopodite greatly 

 enlarged and modified as a raptorial weapon. In Nematoscelis, the 



