HERMIT CRAB AND PKLTOGASTER. 601 



Lately, also, the study of the effects of tlie parasitism of 

 various members of the Rhizocephala ou crustacean hosts has 

 been continued by Mr. G. W. Smith, of New College, Oxford, 

 and I am permitted to make a preliminary reference to his 

 results, which will shortl}'^ appear in a work on the Rhizocephala 

 in the Naples series of monographs. Two most important 

 points are clearly indicated which place our knowledge of this 

 phenomenon on an entirely fresh footing. The capability of 

 assuming the secondary sexual characters of the other sex is 

 shown to be in the cases studied really confined to the male, 

 and, as proved by experiment and observation, modified 

 males (and, apparently, males only) may, on recovery from 

 parasitism by Sacculina, regenerate a completely hermaphro- 

 dite gonad. This examination of parasitic effects in the 

 hermit crab was undertaken at the suggestion of Mr. Smith, 

 to whom I am greatly indebted for much kind help, with the 

 object of ascertaining whether evidence supporting and ex- 

 tending these remarkable results could be derived from the 

 study of other cases. 



Before commencing the description of the effect which the 

 parasite Peltogaster produces upon its host it will be well to 

 mention a few facts with regard to its life history. It belongs 

 to the Rhizocephala, and after completing its free-swimming 

 existence as a Cypris larva passes through a completely in- 

 ternal stage in the body cavity of the hermit crab, like that 

 described by Delage and confirmed by Smith in Sacculina. 

 The Peltogaster internus, which is constituted of a rami- 

 fying root system and a small central tumour, which later 

 forms the external body of the adult, was first discovered by 

 Pekarsky (6), and has also been found on some few occasions 

 both by Smith and myself. With regard to the duration of 

 existence of the internus stage we are still ignorant, owing to 

 the absence of success attending attempts to raise Peltogaster 

 larvfB and artificially infect hosts, and also to the comparative 

 rarity in nature of crabs containing it. When, however, the 

 Peltogaster is ready for emergence to the exterior it need not 

 wait for the assisting agency of a moult, but may, as we have 



