18 ANIMAL PARASITES AND MESSMATES. 



Professor Semper has recently observed pinnotheres in 

 holothurians at the Philij^pine Isles, and Mons. Alphonse 

 M. Edwards has described some from New Caledonia 

 (P. Fischerii) ; so that these little crabs, the friends of the 

 molluscs, are known in both hemisx^heres. 



Do not these conditions seem to authorize the con- 

 clusion that the same thought has presided over the 

 appearance of all living creatures ; that they have all 

 come into existence, not according to the chance ar- 

 rangement of surrounding media, but according to the 

 laws established from the very origin of all things ? 



The shell which lodges both these pinnotheres, in the 

 Mediterranean as well as the Atlantic, is a large acepha- 

 lous mollusc, known under the name of Jamhonneau 

 (a small ham or gammon), and which, according to 

 Aristotle, harbours two different kinds of messmates. 

 This illustrious natural philosopher also described a Pon- 

 tonia {Pontonia custos, Guerin — P. Pyrrhena, M. Edw.) 

 about an inch and a half long, of a pale rose colour, 

 more or less transparent, and which lives with its com- 

 panion, the pinnothere, in the cavity of the Pinna 

 marina. This is the same animal which a naturalist of 

 the last century named the Cancer custos. 



We have wished to ascertain whether Pliny knew 

 these crustaceans. He has spoken of them in the fol- 

 lowing terms : — " The Chama is a clumsy animal with- 

 out eyes, which opens its valves and attracts other fishes, 

 which enter without mistrust, and begin to take their 

 pastime in their new abode. The pinnothere seeing his 

 dwelling invaded by strangers, pinches his host, who 

 immediately closes his valves, and kills one after another 

 these presumptuous visitors, that he may eat them at 

 his leisure." 



