of the Genus Equoree. 381 
bited to us by most of the other productions of the animal 
kingdom ! 
In both cases, the progress of the phenomena is simi- 
lar, their modifications are comparable, and their results 
are equally useful and equally indispensable to the preserva- 
tion of the beings which produce them. In this way, by 
the play of their Jungs and gills, the mammiferz and 
fishes can renew the portion of air or liquid which sur- 
rounds or penetrates them: in the same way also, by alter- 
_ Nate contractions and dilatations of their umbrella, the 
meduse have the faculty of replacing by means of new 
water that which is immediately in contact with them ; 
and this change is perhaps still more indispensable to them 
than to the animals wiih which we compare them in this 
respect. The abundance of their excretions is in effect so 
considerable, nature is so particular in this respect, that 
they could not live long, and they would actually die in the 
purest sea-water, if we neglected to change it very often. 
We think there ought to be no hesitation, therefore, 
after the important facts which we have established, in 
granting to the oscillations of the meduse, independently 
of the locomotive power, which is their peculiarity, two 
other analogous functions; the one being the system of 
general contractibility, the other that of the respiration of 
the most perfect animals. 
This interesting analogy does not seem to have escaped 
the ancients: at least we may conjecture thus much from 
the Greek names of Hali Pleumon, Plewmon Alios, Pneu- 
mon Thalassios, Pneumon Thalastios, Pnewmon Thalattios, 
by which Aristotle, Dioscorides, Kiranides-Kirani, and 
some others have designated the meduse. The Romans also 
gave the denomination of Pulmo marinus to these same 
zoophytes, a uame which has since been used by modern 
authors; such as Gyllius, Massarius, Ruellius, Cordus, 
Rivius, Belen, Matthiolus, Aldrovandus, and Merret. The 
Italian naturalists call the medusa Polmone marino, and. 
the English, Dutch, and Germans, know it by the name 
of Sea-lungs. The Powmon marin of the French authors 
refers to the same idea; which rests on facts so simple, and 
on a comparison so natural, that it can scarcely be con- 
ceived that, among the many eminent naturalists who have 
recently written on the medusz, none have directed their 
attention to this curious part of their history. Spallanzani 
himself does not appear to have even suspected the inter- 
esting cognexion in question. 
Every 
