CRUSTACEA OUTER ORGANISATION 



313 



Ontogeny and comparative anatomy enable us to trace back the anterior maxillte 

 of the Malacostraca to the typical biramose foot. In those Malacostraca which pass 

 through free Nauplius and Protozocea stages the maxillae 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 Mysidce (Euphausia, Thysanopus, My sis}) and in a very 

 reduced form in many Decapoda. 



e. The Posterior Maxillae (Fig. 213). 



The posterior maxillae have the same general typical structure as 



3 C 



FIG. 213. Second or posterior maxillae of various Crustaceans. A, Lernaea branchialis 

 (5 (after Glaus) ; ms, edge of the mouth ; md, mandible ; m l5 anterior maxilla ; d, chitinous 

 ridge ; in^a, m^b, anterior and posterior maxillipedes. B, Penaeidan larva (AcetesT) (after Claus). 

 C, Eucopia australis (after G. O. Sars). D, Paranebalia longipes (after G. O. Sars). E, Astacus 

 fluviatilis (after Huxley). F, Cypridina messinensis (after Claus). G, Cirolana spinipes (after 

 Schioedte). H, Cyclops coronatus ; mo, inner ; m 2 &, outer maxillipede (endo- and exo-podite of the 

 2d maxilla). I, Limnocy there incisa, anterior limb (after Dahl). K, Lysianassa umbo (after Goes). 

 L, Lysiosquilla maculata (after Brooks). I, Proximal, II, distal joint of the protopodite ; ki, 

 lacinia interna ; Jce, lacinia externa ; a, b, divisions of the same,; en, endopodite (palp, feeler) ; ex, 

 exopodite (fan plate). In G : fc l5 Lacinia interna ; fc 2 , k 3 , divided lacinia externa ; k, masticatory 

 ridge (lacinia). In L : 1 and 2, joints of the endopodite. :. , 



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



