174 ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



[and not Pinnotheres, meaning one that * hunts the Pinna '], 

 seeing that he also speaks of Pinnophylax, a word of precisely 

 the same meaning. Not only Aristotle, but many succeeding 

 writers of renown, such as Cicero, Pliny, and seemingly Linnaeus 

 himself, accepted the opinion that there was a compact between 

 the mollusc and the crustacean for their mutual benefit. When- 

 ever little fishes swam in between the expanded valves of the 

 mollusc, it was supposed that its companion gave it a little 

 friendly nip, upon which the valves snapped together, the prey 

 was secured, and shared between the confederates. A similar 

 policy was pursued to exclude the intrusion of a dangerous foe. 

 The great antiquity of the belief is attested by the fact that the 

 Egyptians in their hieroglyphics made use of the pinna and crab 

 to symbolize the helplessness of a man without friends. That the 

 belief was untenable was pointed out by many naturalists, from 

 Gesner down to Cuvier, on the ground that molluscs do not feed 

 on little fishes, and that the residence of the crabs within the 

 valves was sufficiently explained by the prevailing softness of 

 the carapace in this family. This indeed applies chiefly to the 

 females, and it is the females that appear to be most frequently 

 found thus domiciled. It is so much the nature of crustaceans 

 to take refuge in any sort of cleft or cranny that the first entrance 

 of the Pinnotheres into any sort of bivalve can be easily under- 

 stood. When the residence proved to be peculiarly secure, the 

 shell of the crab would by degrees lose a hardness that was no 

 longer especially necessary. That the crab may at times be useful 

 to the mollusc seems after all not so very improbable, for at the 

 approach of an enemy so nervous a creature as a crab would no 

 doubt begin to scuttle about, and in this way communicate its 

 terror to its more apathetic companion, which would then natu- 

 rally close its doors against the danger." 



JOINTED-LIMBED ANIMALS (ARTHROPODA) AS 

 MESSMATES 



We are here especially concerned with Insects and Crabs, 

 regarding which groups there is a great wealth of material from 

 which to select, so that only a few examples can be here given, 

 supplementing, for the latter animals, what has just been said 

 about Pinnotheres. 



