Miscellaneous. 79 



a small papilla ; the large chela of the first pair of thoracic feet is 

 rather stronger in the male than in the female. As regards the 

 abdomen, the first segment is destitute of limbs in both sexes. In 

 the female segments 2, 3, 4, and 5 bear, on the left side, appendages 

 formed of a basal joint terminated by two branches. On the second 

 segment the outer branch is shorter than the inner one ; on the 

 third, the two branches are nearly of the same length ; on the 

 fourth, the outer branch is a little longer, and on the fifth segment 

 it is much longer than the inner one. The appendages 2, 3, 4 are 

 constructed to retain the eggs. For this purpose their basal joints 

 bear two tufts of hairs ; the inner branch also presents two tufts of 

 hairs, one at its extremity, the other on a highly developed posterior 

 swelling. 



In the male segment 2 is destitute of appendages, segments 3, 4, 

 and 5 bear on the left side biramose feet, of which the inner branch, 

 which is always without a posterior enlargement, is much smaller 

 than the outer one. The appendages of the fifth segment are very 

 similar in the two sexes. 



The male hermit-crabs infested by Phryxus Paguri are scarcely 

 altered in the thoracic region, except that the large chela may be a 

 little smaller than usual. But the abdomen presents appendages in 

 equal number to those of the female, and constructed absolutely as in 

 the female, although of rather smaller dimensions. 



On opening one of these males with female abdominal feet we find 

 the testis containing spermatophores of much less than the normal 

 size (about one half), and very imperfect spermatozoids. 



I expected to meet with the same phenomena, perhaps even more 

 accentuated, in male hermit-crabs infested by Peltogaster Paguri ; 

 but, astonishing to say, there is nothing of the kind ; and notwith- 

 standing the more profound action which we should be inclined, a 

 priori, to ascribe to the Peltogaster, that Rhizocephalan produces no 

 apparent modification of the external characters of the male sex, 

 although it causes the sterility of its host. 



The female hermit-crabs infested by Peltogaster, on the other 

 hand, are frequently modified, and the modifications of course aff'ect 

 the abdominal feet. The tufts of hairs on the basal joint and the 

 posterior ovigerous projection of the branch disappear more or less 

 completely ; further, the inner branch is generally smaller than 

 the outer one, even in the appendages 2 and 3 ; in one word, the 

 abdominal feet of these castrated females clearly approach those of 

 the male sex. 



Prom what precedes we are led to conclude either that certain 

 Peltogasters attach themselves to the hermit-crabs at a later period 

 than the Phryxi or that the Peltogasters exert a slower action than 

 the Phryxi, and do not prevent the sexual diff'erentiation from 

 being produced, at least in the male sex. The former interpreta- 

 tion, in our opinion, is the more probable. 



Further, the facts just noted seem to indicate that the Phryxi in 

 general attach themselves to the hermit-crabs at an age when the 

 sexual diflerentiation has not been efi'ected, and while the Decapod 

 crustacean still presents the embryonic abdominal feet. Now Fritz 



