PAGURIDEA EVOLUTION OF HERMIT-CRABS 



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hard plates, and re-acquiring, to a greater or less degree, a 

 secondary symmetry of form. But the story of Pagnrid evolu- 

 tion does not apparently stop here. The genus Farcdomis, from 

 the AVest Coast of America, superficially resembles Porcellana, and 

 is held to be descended from such forms as Fylocheles, while isolated 



j4l>.ff 



Ab.6 



Fig. 123. — Four stages in the development oi Eu2iagnrus longicarjms or E. annulipes, x 

 20. A, Ventral view of Zoaea ; B, lateral view of Metazoaea ; C, dorsal view of Glau- 

 cothoe ; D, dorsal view of adolescent stage. Ah. 6, 6th abdominal appendage ; 

 Mxp.l, Mx2J.3, 1st and 3rd maxilHpedes. (After M. T. Thompson.) 



species are known (though not well known), such as Tylasjns, 

 described in the Challewjer Iicjyorts^ which a}ipear to be 

 Pagurids that have deserted their shells. 



The metamorphosis of the Hermit-crabs has recently been 

 studied by M. T. Thompson." 



The Zoaea (Fig. 123, A) differs from that of the Galatheidea 

 mainly in the absence of the long spines. It possesses the usual 

 ^ Vol. xxvii. p. 81. ^ Proc. Boston ,Soc. Xat. ITis'., xxxi., 1904, j). 147, 



