312 



COMPARATIVE ANATOMY 



CHAP. 



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

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

 adult animal. 



d. The Anterior Maxilla (Fig. 212). 



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

 for mastication, like the mandibles and the posterior _ maxillae. The 

 biramose character is much more commonly retained in them than in 

 the mandibles, the exopodite being more frequently present. 



Entomostraca. — PAs/Hoi)OfZ« (D), the anterior maxillfe are reduced to simple 

 nnjointed masticatory ridges without feelers. In the Ostracocla (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 agills (after Brady). 

 B, Cypridina stellifera (after Glaus). 0, Cythera viridis (after Zenker). D, Daplinia simills 

 (after Glaus). S, Eupliausia peUucida, last Calyptopsis stage (after G. 0. Sars). F, Astacus 

 fluvlatilis (after Huxley). G, Euphausia peUucida, adult (after G. 0. Sars). H, Paraneballa 

 longipes (after G. O. Sars). ex, Exopodite ; en, endopodlte ; Ic, masticatory ridge ; ^-j , inner ; 

 ^2, outer masticatory ridge. 



and CytheridcB an exopodite, in the form of a fan-like plate, which is vibratile, and 

 when the maxilla moves promotes respiration. The anterior maxillfe 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 Cirripedia are simple masticatory ridges without feelers ; 

 they are wanting in the RMzocepliala. 



Leptostraca. — The anterior maxilla of Nehalia {H) are provided with two 

 masticatory ridges (lacinice), 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. 



Malacostraoa (£, F, G). — The maxillae are flatly compressed. The exopodite is 

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

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

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



