VI 



PAGURIDEA EVOLUTION OF HERMIT-CRABS 



1/9 



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 Pardlomis, from 

 the West Coast of America, superficially resembles Porcellana, and 

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



Ab6 \ 



FKI. 123. Four stages in the development of />/"/"/''* /p/^/r,//y,/'xc>r I-'., i/i/n/'/i/n'.-., 

 20. A, Ventral view of Xnaea ; B, lateral view of Metazoaea : C, dorsal view of < llan- 

 cothoe ; D, dorsal view of adoleseunt sta^'e. Ab.<j, titli aliduminal a|i|-n.; 

 M. >/>.!, M />..:. 1st and 3rd niaxillii>cdus. (After M. T. Tlioniiisou. ) 



are known (though not well known), .such as 

 described in the ('Imllt'iiyer Jt'rjHir/x, 1 which ajiprar lo he 

 I'agurids that have deserted their shells. 



Tin; metamor])hosis oi' the Hermit-crabs has recently been 

 studied by M. T. Thompson.'-' 



The Zoaea (Fig. 1 -'.', A) differs from I hat >!' i he Galatheidea 

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



1 Vol. xxvii. ]>. 81. 2 I' r<><: Boston Soc. Nat. //is'., xxxi., 1904, \>. 117 



