212 Miscellaneous. 



of the crustacean. The following experiment proves that this is 

 not the case. 



To a hermit-crab that has been starved by fasting for some days 

 there is given a Cardium impregnated with carmine. Immediately 

 the annelid, which is likewise starving, shows itself, it is made to 

 withdraw by being touched with a brush : it is driven away in this 

 manner each time it returns. During this time the crab devours 

 the Cardium and the carmine. After a few hours there is seen in 

 the basin the excrement of the crustacean stained a vivid red. To 

 ascertain whether the annelid has eaten a portion of the faeces, we 

 break the shell and dissect the worm : I have never discovered 

 carmine in its alimentary canal. 



Nenilejyas, therefore, does not devour the excrement of the 

 hermit-crab. This discovery, it seems to me, is interesting from 

 the point of view of the nature of the association between the crab 

 and the annelid. In the opinion of P.-J. van Beneden this is a case 

 of commensalism. Xow, according to the definition of the celebrated 

 zoologist, " the commensal does not live at the expense of its host : 

 all that it desires is a home or its host's leavings ; the parasite 

 instals itself with its neighbour temporarily or permanently ; with 

 or without the latter's consent, it extorts from it board and, very 

 often, lodging." This last definition applies admirably to the case 

 of JSereilepas. The creature evidently injures the hermit-crab, since 

 it abstracts a considerable portion of the latter's food: it is a 

 veritable parasite, in the sense in which the word is understood in 

 ordinary language. 



• Pinnotheres, another commensal, which is equally well known, 

 leads us to identically the same conclusion. On dissecting the 

 stomachs of specimens of Pinnotheres and those of the Acephala with 

 which they live I have discovered the presence of the same sub- 

 stances, composed for the most part of lower forms of plant-life. 

 There is not, as certain rash hypotheses would endeavour to make 

 us believe, a division of the particles into two groups : the animal 

 particles for the Pinnotheres and the vegetable ones for the moUusk. 

 On the contrary, the Pinnotheres diverts for its own benefit a portion 

 of the food-matter intended by the mollusk for itself. Although 

 the injury may be very slight, it exists none the less. It matters 

 little whether' the food-matter be abstracted in the alimentary 

 canal itself, as is done by Tcmia, Echinorhynclms, and many Nema- 

 todes, or at the entrance of the mouth ; on the same grounds that 

 the Hclminthes, which do not attack the tissues, are parasites of 

 th.eir host, Pinnotheres is a veritable parasite of its mollusk, as is 

 JS'ernlejjas of the hermit-crab. This is the conclusion at which it 

 was my desire to arrive ; by the study of other commensals it will 

 doubtless be strangely extended. — Comjjtes Rendus, t. cxix. no. 13 

 (tSeptember 24, 1894), pp. 540-543. 



