166 M. Valenciennes on Fishes and Reptiles. 
of the water, or whether (what is more singular. in a physio- 
logical sense) their respiratory organ being branchial, they 
can respire only through the medium of water. 
In the first case, nothing can have a more completely ma- 
rine form than the Cetacea; whales, dolphins, and porpoises ge- 
nerally belong to the sea, but we have the Platanista of Pliny,* 
which lives in the water of the Ganges above Benares, to which 
the water of the sea never ascends. Porpoises (Toninas) are 
found in the Orinoco above the cataracts of Atures and May- 
pures, and the Beluga of Steller occurs in lakes and places 
where the water is fresh. So much, then, for the Cetacea. 
Among the mammifera, the seals likewise afford us another 
example of animals generally marine occurring also in fresh 
waters; thus they are met with in lake Baikal, in the small 
lake Araly and in the Caspian Sea, which, being ‘ess salt than 
the sea, may just as well be considered a collection of fresh 
water as a sea, or at least it forms a passage or connecting 
link between the two. 
I need not say any thing to you respecting aquatic birds ; 
but among reptiles no form can appear more peculiarly adapt- 
ed to fresh waters than Crocodiles, and it is in fact in all the 
great rivers of Africa, Asia, and America, that they take up 
their abode. But the Crocodilus biporcatus which mhabits 
the Sechelles, and others of the small islands of the Amirantes, 
as well as the other islands of Polynesia, Timor, Ceram, &c., 
swims in the sea, and obtains its food there. We must not, 
in a discussion of this kind, insist upon the difference of 
species, for those slight modifications of form which we seize 
upon, and to which we assign that importance which they 
really ought to possess in the determination of species, do not 
affect the basis of organization. It is of small consequence 
that there are two projections on the muzzle of the Crocodilus 
biporcatus, and that the same part in the crocodile of the Nile 
is smooth ; both of them are still crocodiles, formed on the 
same type of organization, breathing, moving, and feeling 
alike. Accordingly, when we find the Crocodilus biporcatus 
on the coast of Coromandel, where there is a great conflux of 
fresh water, the animal lives in the rivers. 
* The Platanista of Pliny is by some authors considered to be the Delphi- 
nus gangeticus of modern zoologists. 
