162 = = Onthe Natural History of the Dugong, ; 
toeach. The fishes, destined to live exclusively in the ocean, are 
provided with a comparatively external mechanism, (the branchie 
or gills,) over which the surrounding fluid flows, to impart its oxy- 
gen to the blood. The terrestrial vertebrata breathe by means of 
Jungs, inspiring and expiring the cireumambient air. And some re- 
markable reptiles, as the proteus and siren, created with a capacity 
for living in either of these media, are possessed of both those or- 
gans by which the terrestrial and aquatic tribes respire. 
It would be impossible for any animated being to contain, in the 
ordinary bulk of a respiratory organ, that surface which would be 
requisite to extract from water a quantity of oxygen suflicient to 
maintain the temperature possessed By warm-blooded animals : 
lungs, in which, over a large surface, and at intervals, the oxygeni- 
ferous medium can be diffused, are indispensable to these classes. 
But the function of respiration by lungs is impracticable to animals 
which are constantly submersed ; whence fishes respire by gills, and 
are cold blooded. 
It cannot, then, fail to strike the observer with surprise, when he 
discovers in the ocean a large tribe of warm-blooded, mammiferous 
animals, analogous to fishes in their external form, with the fin and 
‘the hairless coat, and pursuing a similar mode of life. And wonder 
will increase, when examination proves, that they are nothing else 
than terrestrial mammalia, whose internal organs are concealed 
under the figure of the fish. Speculation immediately suggests the 
geological fact, that fishes existed prior to the creation of mamma- 
lia; and that the Omnipotent has passed by slow gradations from 
one series of organization to another ; that the type or model on 
which all vertebrated animals are formed, is essentially the same ; 
and the train of ideas may be easily extended to the conception, 
‘that those internal differences which were necessary to the terres- 
trial mammalia, were first attempted in the inhabitants of the ocean. 
The Cetacea, of which the whale (Cete) serves as an example, re- 
spire by means of lungs, incessantly rising to the surface for atmo- 
spheric air: they are viviparous, and suckle their young, and the 
sexes associate in the manner of terrestrial animals.. The bones 
which represent those of the anterior limbs of quadrupeds, are con-- 
cealed under thick tendinous envelopes in the form of pectoral fins ; 
the posterior members are displaced by the cartilages of a horizon- 
tal caudal fin ;* and the pelvis is in a rudimentary state. | 
- Some striking peculiarities present themselves in the general er- 
ganization of the cetacea. Constantly immersed in the water, with 
the exception of a small portion of the body,t it became necessary 
te the act-of respiration, that the nostrils should have a direction 
differing from terrestrial mammalia; and we find in the cetacea, 
* The cetacea differ from fishes in the direction of the caudal fin ; in the 
latter it is always vertical. 
“ce His delights 
Were-dolphin like; they shew’d his back above 
The element they liv’d in.”—SHAKESPEARE. 

