FREE MESSMATES. 33 



Ilypcrhia Latreillli, lodged in the superb lihizostoma, 

 which regularly appears in the later season of the year 

 on the coast of Ostend; and a long time since, in 1776, 

 0. F. Miiller gave to a species of this genus the name of 

 Hyperina mcdusarum. Mr. Alexander Agassiz once 

 found a Hyperina on the disc of smAurelia. The medusa, 

 when extended, forms for them a balloon with its 

 parachute, which supports and conveys them with 

 greater or less rapidity. Professor Mobius has but 

 lately remarked the presence of Hyperina galha, Mont., 

 in the Stomohrachium octocostatum, Sars, a small species 

 of medusa which appears in the Bay of Kiel in October 

 and November. This naturalist supposes that these 

 messmates at first inhabited the Medusa aurita, and 

 then migrated into this species. 



Besides these, there are Gammari, which, according to 

 Semper, live in the Avicula meleagrina (pearl mussel), 

 and are perhaps the principal manufacturers of fine 

 pearls. The immense buccal cavity of the fishing-frog 

 {Lophins piscatorius) is the abode in the Mediterranean 

 of an Apterychta, and in the Northern Ocean of a curious 

 amphipod of the ordinary size of the Gammarus, which 

 takes a voyage without expense, and with no fear of 

 wanting provisions. My son discovered it at Ostend, 

 and proposes the name of Lopliiocola to distinguish it. 

 The Gammari give lodging themselves to a great 

 quantity of parasites, which they must introduce into 

 the bodies of those to whom they serve as food. It 

 has been long known that whales have lice, to which 

 naturalists have given the name of Cyami. They are 

 found on the whales of both hemispheres, and on some 

 other cetaceans. It is very remarkable that they are 



