44 ANIMAL PARASITES AND MESSMATES. 



carapace, and which, as true messmates, give themselves 

 up to the caprices of their host. These are a kind of 

 Spirorbis, which, under the form of small spiral tubes, 

 instal themselves, by preference, on the limbs, the 

 antennae, or the claws. 



Mr. A. Agassiz has seen on the coast of the United 

 States, a Beroe (Mnerniopsis Leidyi) which gives lodging 

 in its interior to worms which somewhat resemble the 

 Hirudinidse, and which doubtless live there as mess- 

 mates. Mr. A. Agassiz has remarked to me another 

 example of commensalism. On the coast of the territory 

 of Washington, as far as California, is found a worm 

 of the genus Lepidonotus, which always lives near the 

 mouth of a star-fish, the Asteracantkion ochraceus of 

 Brandt ; sometimes as many as five are found together 

 on a single individual, and are placed on different parts 

 of the ambulacral rays. Mr. Pourtalis and Mr. Verril 

 have observed annelids lodged in the polypidoms of the 

 Stylaster. 



There are few fish on which are not found Caligi, 

 charming crustaceans which please the eye by their 

 attenuated shape and their graceful movements. On 

 these Caligi, which sometimes literally cover the skin of 

 cod-fish coming from the north, we often find a curious 

 trematode, the Udonella, which resembles one of the small 

 hirudinidse. Should this worm be placed among mess- 

 mates? What is the part which it plays? We are 

 persuaded that it is the same as that of the histriobdelhe 

 under the tail of lobsters, that is to say, that it clears 

 off the eggs of caligi which do not arrive at perfection, 

 but perish in the course of their evolution. 



Boussel de Vauzeme has mentioned another worm, a 



