HERMIT GRAB AND PELTOGASTER. 609 



tjpe^ but in tlie second and third appendages the develop- 

 ment of the internal ramus was quite slight, while in the first 

 it had attained about a half of its usual size. 



The consideration of some facts dealing with the later 

 metamorphoses of the hermit crabs may help us to decide 

 whether these cases fall under the heading of true modifica- 

 tion or retardation of development. 



The life-history of Eupagurus meticulosus is not 

 known in detail, but that of the American species, E. longi- 

 carpus, has been the subject of careful research by Thomp- 

 son (8). This species as noted above differs from E. meti- 

 culosus in the loss of the first abdominal appendage by the 

 male. 



After escaping from maternal gestation the larva leads a 

 pelagic life, the last stage of which is known as the Ghxu- 

 cothoe. In this the animal has an appearance and anatomy 

 nearly similar to the adult, but the abdomen is symmetrical 

 in form, and it also differs in the possession of a pair of 

 appendages for each segment. These are of male type, 

 though the rami are but slightly developed. 



In the stage, after the moult from the Glaucothoe, during 

 which the animal seeks a shell, the abdomen becomes asym- 

 metrical, the appendages of the right side are totally lost, 

 and the first appendage of the left becomes rudimentary, 

 while throughout the remaining appendages the external 

 ramus increases in size. At this time there is no differentia- 

 tion of sex, both male and female possessing appendages 

 with a rudimentary internal ramus. And it is not till thirty 

 days after the glaucothoe stage that the rudiment on the 

 second segment even begins to develop into a typical female 

 appendage. Ten days after that the alteration to the female 

 type begins in those of the third and fourth segments, but 

 the complete development requires several further moults. 

 Quoting Giard's case of the parasitism of Peltogaster on 

 Eupagurus bernhardus, where the form of the appen- 

 dages of the female is said to approximate to the male type, 

 Thompson says, " The parasite presumably might attach 



