DECAPODA. 521 



the shaft are folded on themselves, and the two flagella are much 

 abbreviated (Fig. 316 Ant. 1 ). 



The second antenna consists typically of a two-segmented pro- 

 topodite, a scale-like exopodite (scaphocerite), and of an endopodite 

 ending in a flagellum. The proximal segment (coxopodite) bears 

 the orifice of the green gland on a prominence (Fig. 314 Doe). 

 The second segment (basipodite), is often divided longitudinally, 

 when the exopodite is present, into two parts. The exopodite, 

 though retaining its flagellar character in the larvae of some of 

 the lower Decapods, is, when present in the adult, an undivided 

 scale-like structure, often ending in a spine. It presents many 

 phases of reduction and in the Scyllaridae and Brachyura is 

 absent altogether. The endopodite has two large basal segments, 

 the proximal articulating with both divisions of the basipodite, 

 and a many-jointed flagellum. When the exopodite is absent 

 the appendage presents a 4-segmented shaft ending in a flagellum. 



The Scyllaridae are remarkable in that the coxopodites of the 

 second antennae have become completely fused with theepistome, 

 and, except for a faint median division, with one another. 



In the Brachyura these appendages are much reduced, and the 

 basipodite is often completely fixed between the epistome and 

 the pleural margin (Fig. 316). The coxopodite appears to be 

 still recognizable as the small opercular flap covering the orifice 

 of the green gland. Other modifications of the second antennae 

 and their relation to the orbits are described above (p. 516). 



The mandible is generally robust, and the palp well developed, 

 though the latter is absent in several families of the Caridea. 



The first maxilla is produced imvards into two lobes, referred 

 by Hansen (see p. 438) to the first and third segments of the 

 limb. 



The second maxilla is like wise produced in wards into two lobes, 

 both deeply divided (Fig. 240, d, p. 346). The palp, though 

 two jointed in some larvae, is unsegmented in the adult. The 

 exopodite is expanded into a long plate, the scaphognathite, 

 which, lying, as we have seen, in the channel of the outgoing 

 water, effects, by its movements, the renewal of water in the 

 branchial chamber. 



The three anterior pairs of thoracic legs of Decapods have, 

 for the most part, lost their locomotory function in the adult 

 and are modified, as maxillipeds. Hence there are only five 



