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may present many individuals of the same species of these 
parasite Crustacea. “ The pinnae,” says Aristotle, “ have 
in their shell the animal called the guardian of the pinna ; 
it is a small squilla or cancer, which they cannot lose with- 
out perishing speedily.” He adds a little lower, “ There 
are born in some testacea, certain white crabs, and very 
small. The greatest number is found in those species of 
muscles whose shell is inflated. After this comes the pinnae ; 
its crab is named pinnotheres . Some are also found in cockles 
and oysters. These little crabs have no sensible growth, and 
the fishermen assert that they are formed at the same time as 
the animal with which they inhabit.” He again tells us, a 
little further on, “ that there are born in the cavities of sponges 
some small crabs, similar to the guardian of the pinna) ; that 
they are there like the spider in its retreat; and that by open- 
ing and closing these cavities at proper times, they can catch 
there the little fishes. They keep them open to cause the prey 
to enter, and close them immediately when it has got in.” 
It is certain that the muscles, cockles, and oysters of our 
coasts, previously cited by Aristotle, enclose, at least at a cer- 
tain period of the year, some small Crustacea, generally known, 
similar in all respects to those which, according to him, and 
many other ancient authors, inhabit the shell mollusca, and 
with which the genus pinnotheres has been established ; that 
these shell-fish do not habitually present other animals of the 
same class ; that there are often found in certain pinnae, either 
other pinnotheres larger than the preceding, or small candies . 
We also know that some paguri and porcellanae lodge in 
sponges ; and it is probably to these Crustacea that Aristotle 
alludes, in the passage last cited. But it is not proved that 
the father of zoology was right in advancing that the guardian 
of the pinnae was either a little crab, or a little squilla, or 
caridion. According to M. Cuvier, this disjunctive expres- 
