602 F. A. POTTS. 



actually witnessed, dissolve its way through the soft skin of 

 the abdomen. In the external stage the Peltogaster is a suffi- 

 ciently sti-iking object with its sac-like body of a clear red 

 colour and the great mass of dark green roots shining through 

 the semi-transparent skin of the host. Practically always it 

 is found in the same position of fixation between the second 

 and third abdominal segments on the left-hand side of the 

 body, occupying in a noteworthy way the space where, in the 

 normal female, the embryos are borne. Once become external 

 the adult size is quickly attained, and this latter, then, is no 

 indication of the age of the parasite, but only of the food- 

 supplying capabilities of the host. The same crab frequently 

 supports two Peltogasters, and less often examples of the 

 Cryptoniscid Liriope pygmse a, are found fixed on or near 

 the Peltogaster itself. But neither the size of the Peltogaster 

 nor the presence of one, or a plurality of parasites appear to 

 be correlated with the degree of modification, due to the para- 

 site, which I go on to describe. It may, however, be men- 

 tioned here that the character of the root system of the para- 

 site seems to change with the duration of infection, being more 

 diffuse and extensive in the earlier stages, and more con- 

 densed, compact, and dark coloured as time goes on. 



II. General Effect of the Parasitism op Peltogaster 



ON EUPAGURUS. 



Parasitic castration has been studied by Giard amongst his 

 numerous other cases, also in the genus Eupagurus (2). At 

 Wimereux the occasioning parasites are the Bopyrid Phryxus 

 and the Cirripede Peltogaster (P. paguri), and these are 

 found on Eupagurus bernhardi. At Naples one of the 

 most frequently occurring species of hermit crab is E. meti- 

 culosus,^ very common at a depth of 10 metres, and 20 — 30 



' A small percentage of the crabs examined, infected and uninfected, 

 appear referable to the species E. angulatus, which is distinguished from 

 E. meticulosus by certain characters of the chela. Yet intermediate 

 specimens are found, and tlie effect of the parasite is the same as in E. 



