HERMIT CRAB AND PELTOGASTER. 611 



third, fourth, and fifth segments in the male. In the female 

 appendages are found on the second, third, and fourth seg- 

 ments, of the usual biramous type. One of three individuals 

 with Peltogaster was a female; in it I was unable to detect 

 any alteration from the female type. Of the two males one 

 was unaltered; the other was provided with three pairs of 

 abdominal biran]ous appeudages exactly as in the female. 

 But these appendages, though of an exact female form, did 

 not possess the long hairs which serve as egg attachments in 

 the female, and were only about one third the size of those 

 of a slightly smaller normal female with which it was com- 

 pared. It may be mentioned that the modified male was 

 much smaller than the unmodified, but the examination of a 

 more considerable number of cases is needed before the 

 connection of modification with infection at an early stage is 

 asserted. 



Evidence concerning the Pekmanence of the Modification 

 CAUSED BY Parasitism. 



(1) From moulting. 



(a) A large number of iufected crabs, particularly un- 

 modified males, were kept in aquaria and fed generously. 

 In periods varying from a fortnight to two months the crabs 

 moulted, and in no cases, either of infected females or males 

 of any degree of modification, was there any alteration of the 

 relative proportions of the two rami in the new appendage. 



(b) Primarily, for another purpose, to be treated of below, 

 operations were made on a large number of crabs, the 

 external part of the Peltogaster being removed by scissors. 

 They were then kept as far as possible in natural surround- 

 ings and well fed, and after a mouth moults became of 

 frequent occurrence. On comparing the old and new append- 

 ages no difference in the relative proportion of the rami, 

 concurrent with the removal of the occasion of modification, 

 could be distinguished. It is interesting to compare the 



