CRUSTACEA EUCARIDA DECAPODA 



CHAP. 



reduction (Fig. 122, B) and disappearance (C) of these original 

 plates, their place being taken first by a number of irregularly 

 situated small spines and warts, which, however, subsequently fuse 

 up to form definite segmental plates. In Lithodes maia, <$ (D), 

 there are a series of lateral and marginal plates, while in 

 Acantholitlius (E) a number of median plates appear, presum- 

 ably by the fusion of the small spines present in the median 



A B C 



122. Diagrams of abdomen : A, of Pylopagurtis, sp. ; B, of Hapalogaster cavicauda ; 

 C, of 1>< i -mill a fas /tixjiii/Hx ; D, of I.i/limlfa Mit in, << : E, of Acantholithus 

 Ji i/xt fi.i: c, Central plates; /, lateral ] dates ; in, marginal plates; T, telson ; 

 1-6, lst-6th abdominal segments. (After Bouvier.) 



line in .Lillmili's maia; finally, a fusion of the marginal and 

 lateral plates may take place, so that each abdominal segment 

 is covered by a median and two paired lateral plates. 



It is to be noted iliat the males and females of the various 

 species do not follow a parallel course of development, the plates 

 in the male being symmetrical, while those of the female are 

 ol'ieii highly asymmetrical (compare Figs. 122, D, and 121), thus 

 giving the strongest evidence of a 1'agurid ancestry. 



AY/y///.s and the Lithodidae, then, are Pagurids which have 

 jiven up living in shells, and have become adapted to a free 

 existence, protecting their soft parts by the development of 



