PAGURIDEA EVOLUTION OF HERMIT-CRABS 



179 



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

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

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

 the West Coast of America, superficially resembles Porcellana, and 

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



Ab.6 



FIG. 123. Four stages in the development of Eupagurus longicarpus 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. Ab.6, 6th abdominal appendage ; 

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



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

 described in the Challenger Reports} which appear to be 

 Pagurids that have deserted their shells. 



The metamorphosis of the Hermit-crabs has recently been 

 studied by M. T. Thompson. 2 



The Zoaea (Fig. 123, A) differs from that of the Galatheide-a 

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

 1 Vol. xxvii. p. 81. 2 Proc. Boston Soc. Nat. 7//s'., xxxi., 1904, p. 147, 



