312 



COMPARATIVE AX ATOMY 



CHAP. 



the Copepoda (more especially the latter) still retain in the structure of the man- 

 dibles the original typical biramose form, since they alone retain the exopodite in the 

 adult animal. 



d. The Anterior Maxillse (Fig. 212). 



These lie, in all Crustaceans, close to the mouth, and serve chiefly 

 for mastication, like the mandibles and the posterior maxilla?. The 

 biramose character is much more commonly retained in them than in 

 the mandibles, the exopodite being more frequently present. 



Entomostraca. Phyllopoda (D), the anterior maxillae are reduced to simple 

 unjoin ted masticatory ridges without feelers. In the Ostmcoda (B, C] also the mas- 

 ticatory ridge is the principal part, but there is a feeler as well, and in the Cypridce 



FIG. 212. Anterior maxillae of various Crustaceans. A, Notodelphys agilis (after Brady). 

 K, Cypridina stellifera (after Glaus). C, Cythera viridis (after Zenker). D, Daphnia similis 

 (after Glaus). E, Euphausia pellucida, last Calyptopsis stage (after G. O. Sars). F, Astacus 

 fluviatilis (after Huxley). G, Euphausia pellucida, adult (after G. O. Sars). //, Paranebalia 

 longipes (after G. O. Sars). ex, Exopodite; en, endopodite ; A-, masticatory ridge; A-J, inner; 

 to, outer masticatory ridge. 



and G'i/thcrid(c an exopodite, in the form of a fan-like plate, which is vibratile, and 

 when the maxilla moves promotes respiration. The anterior maxillre of the free- 

 living Copepoda (A) have masticatory ridges, feelers, and sometimes also fan-like 

 exopodites ; in the parasitic forms, on the contrary, these parts are much reduced. 

 The anterior maxillae of the Cirripcdia are simple masticatory ridges without feelers ; 

 they are wanting in the Rhizocephala. 



Leptostraca. The anterior maxillre of Ncbalia (H) are provided with two 

 masticatory ridges (lacini?e), and carry a long, jointed, whip-like appendage, which 

 is regarded as an endopodite. This is bent backward dorsally, at least in the 

 female, and serves for cleaning the inside of the shell fold. 



Malacostraca (E, F, G}. The maxilhe are flatly compressed. The exopodite is 

 often wanting. The distal joint of the protopodite carries a masticatory ridge 

 (lacinia interim), and so does the basal joint of the endopodite (lacinia externa). 

 The remaining one or two joints of the endopodite form the feeler (palp). 



