FKEE MESSMATES. 51 



Mr. Albany Hancock found twelve species of Clione on 

 a single Tridacna. They are evidently not parasites, 

 and I am not sure if their place is properly among 

 messmates. The oyster, and more especially the Ostrea 

 hippopus, lodges three or four different sorts in its shell. 

 These Cliones possess siliceous spicules, by means of 

 which they hollow out galleries in the substance of 

 shells. Mr. Hancock has published a monograph of 

 this genus, in which he recognizes twenty-four species 

 collected from different shells, and two other species, 

 which he refers to the genus Thoasa. 



The cliones are real lodgers which lead us to the 

 Saxicavte, the Pholades, and the Teredines; they seek 

 their lodging in rocks or in wood; these lead directly 

 to the sea-urchins, which also hollow out lodgings in 

 rocks, but without penetrating deeply. Professor Allman 

 has just observed a very remarkable case of commen- 

 salism between a sponge and one of the tubulariae. 

 The crown of the tubularia is extended at the entrance 

 of the canals of the sponge; and the association is so 

 complete, that the Edinburgh professor imagined that 

 he had before his eyes a true sponge with the arms of a 

 tubularia. 



In the lowest ranks of the animal scale, there are 

 certain kinds of animalcules, which establish them- 

 selves on the bodies of obliging neighbours, and take 

 advantage of their fins in order to swim at then: expense. 

 Thus we often find the bodies of certain crustaceans 

 covered with a forest of vorticellse and other infusoria. 

 They cause themselves to be towed like cirrhipedes, but 

 they do not change their toilet like them, so that it 

 cannot be said that they put on the livery of servitude. 



