174 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
[and not Pnnotheres, meaning one that ‘hunts the Pzxna’], 
seeing that he also speaks of Pzxnophylax, a word of precisely 
the same meaning. Not only Aristotle, but many succeeding 
writers of renown, such as Cicero, Pliny, and seemingly Linnzus 
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 Prxnotheres 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. 
