16 ANIMAL PAEASITES AND MESSMATES. 



which tempts them, but the desire of having always a 

 secure retreat in every place. The pinnothere is a 

 brigand who causes himself to be followed by the cavern 

 which he inhabits, and which opens only at a well-known 

 watchword. The association redounds to the advantage 

 of both ; the remains of food which the pinnothere aban- 

 dons are seized upon by the mollusc. It is the rich 

 man who instals himself in the dwelling of the poor, and 

 causes him to participate in all the advantages of his 

 position. The pinnotheres are, in our opinion, true 

 messmates. They take their food in the same waters as 

 their fellow-lodger, and the crumbs of the rapacious 

 crabs are doubtless not lost in the mouth of the peaceful 

 mussel. There is no doubt that these little plunderers 

 are good lodgers, and if the mussels furnish them with 

 an excellent hiding-place and a safe lodging, they them- 

 selves profit largely by the leavings of the feast which 

 fall from their pincers. Little as they are, these crabs 

 are well furnished with- tackle, and advantageously 

 placed to carry on their fishery in every season. Con- 

 cealed in the bottom of their living dwelling-place (a 

 den which the mussel transports at will) they choose 

 admirably the moment and the place to rush out to the 

 attack, and always fall on their enemy unawares. Some 

 of these pinnotheres live in all eeas, and inhabit a 

 great number of bivalve molluscs. The northern seas 

 contain a large species of Modiola (Modiola Papuana) 

 which is especially found in deep and almost inaccessible 

 parts, and which always encloses a couple of pinno- 

 theres about the size of a hazel-nut. We have opened 

 hundreds of these modiolas, and we have never met with 

 any without their crabs. We have long since deposited 



