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may present many individuals of the same species of these 

 parasite Crustacea. " The pinnoe," says Aristotle, " have 

 in their shell the animal called the guardian of the pinnm ; 

 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 pinnse ; 

 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 pinnae ; 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 caridicE. 

 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- 



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