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 

 Spirorhis, which, under the form of small spiral tuhes, 

 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 {Mnemiopsis Leidyi) which gives lodging 

 in its interior to worms which somewhat resemble the 

 Hirudinidae, 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 Asteracanthion ochraceus of 

 Brandt ; sometimes as many as five are found together 

 on a single individual, and are placed on different parts 

 of the ambulacral isijs, Mr. Pourtalis and Mr. Verril 

 have observed annelids lodged in the polypidoms of the 

 Stylaster. 



There are few fish on which are not found Callgi, 

 charming crustaceans which ]3lease the eye by their 

 ,/ ! attenuated shai^e and their graceful movements. On 

 ^ I these Caligi, which sometimes literally cover the skin of 

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

 I trematode, the Udonella, which resembles one of the small 

 I 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 histriobdellae 

 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. 



Roussel de Vauzeme has mentioned another worm, a 



