CRUSTAGEA—OUTER ORGANISATION 



313 



Ontogeny and comparative anatomy enable us to trace back tlie anterior maxillfe 

 of the Malacostmca to the typical biramose foot. In those Malcteostmca which pass 

 through free Nauplim and Protozocea stages the maxillfe are distinctly recognisable 

 as consisting of a protopodite with a masticatory ridge on the distal joint, an en- 

 dopodite of two or more joints with a masticatory ridge on the basal joint, and an 

 exopodite in the form of a fan-like plate. The exopodite is retained as a vibratile 

 fan-like plate in most Mi/sidcc (Euphausia, Thysanopus, Mysis), and in a very 

 reduced form in many Decapoda. 



e. The Posterior Maxillae (Fig. 213). 

 The posterior maxillas have the same general typical structure as 



Fio. 213.— Second or posterior maxillse of various Crustaceans. A, Lernsea branchialis 

 {J (after Glaus) ; wis, edge of the mouth ; md, mandible ; mi, anterior maxilla ; d, chitinous 

 ridge ; wi^a, m2&, anterior and posterior maxillipedes. B, PenEeidan larva {Aceiesi) (after Glaus). 

 C, Euoopia australis (after G. O. Sars). D, Paraneballa longlpes (after G. O. Sars). E, Astaous 

 fluvlatilis (after Huxley). F, Oypridina messineusis (after Glaus). G, Girolana spinipes (after 

 ScMoedte). if, Gyolops coronatus ; m.2«, inner; moft, outer maxillipede(endo- and exo-podite of the 

 2d maxilla). J, Limnocytliere incisa, anterior li mb (after Dahl). K, Ly sianassa umbo (after Goes) . 

 L, LysiosquiUa maculata (after Brooks). /, Proximal, /7, distal joint of the protopodite ; lei, 

 lacinia interna ; 7k, lacinia externa ; a, 6, divisions of the same.; en, endopodite (palp, feeler) ; ex, 

 exopodite (fan plate). In G : fci, Lacinia interna ; 7c2, 7:3, divided lacinia externa ; fc, masticatory 

 ridj^e (lacinia). In L : 1 and 2, joints of the endopodite. 



the anterior, and like the latter serve for mastication. But they 



