564 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Besides the Hymeniacidon occasionally found with 

 E. bernhardus, a species of Suberites (probably 

 S. domuncula) not infrequently occurs in connection 

 with E. pubescens. The sponge often completely 

 absorbs the original shell of the hermit crab, leaving the 

 crustacean in a smooth cavity in its interior. This 

 crab is also found with the same Hymeniacidon which 

 has already been mentioned in connection with 

 E. bernhardus. 



Some tropical forms which utilise the cavities found 

 in corals and sponges can hardly be included under this 

 section. 



Parasites. 



I have found no internal parasites in the species 

 under consideration, and I do not believe any have been 

 recorded. Three external parasites are known. In the 

 branchial chamber the Isopod Bopyrus is found, and on 

 the abdomen Phrywus paguri and the degenerate 

 Cirripede Peltogaster paguri. 



As the last-named parasite has a remarkable and 

 well-known effect on the generative organs of its host, 

 it might be useful to summarise briefly the results of 

 investigations which have been made on the subject.* 



The infection by Peltogaster has the immediate 

 effect of diminishing the size of the gonads, and at an 

 early stage ova make their appearance in the glandular 

 part of the testis. The male secondary sexual characters 

 are stimulated to development towards the female type, 

 and if the female is infected early a retarding influence 

 is exerted by the parasite on its attainment of sexual 

 characters. If the parasite be extirpated the modifica- 



* F. A. Potts. Q.J. M.S., Vol. L., pt. 4, Nov. 1906, p. 599. 



