,§4 OF CARTILAGINOUS FISHES. 
the animal kingdom. It would appear that they are ca- 
pable of fubfifting indifcriminately in either of thefe two 
elements, to each of which the ftructure of their parts 
j'eem to- have a reference ; it was no doubt this afpeft of 
the cartilaginous fiihes, which prefented itfelf to Linnavs 
when he arranged them in the fame order with thofe ani- 
mals, properly amphibious *, that are capable of fubfifting 
cither in the water or in the air. Of this power, however, 
this clafs of beings is by no means poffefled ; for, though 
they are capable of fupporting life for a longer time on 
lhore, than the fpinous fifties, yet there is hardly any of 
them that can live there above a few hours at a timef. 
Whatever, therefore, be the ftrafture of their organs, 
there is none of them properly amphibious, or that juftly 
merits a place among that order of beings. 
But although the double ftru&ure of the organs of 
refniration in the cartilaginous fifties, will not juftify us 
in placing them among the fillies, tortoifes, lizards, and 
other animals that are ftri&ly amphibious, it forms, 
however, a very palpable mark of diftiu&ion between 
them and the cetaceous fifties on the one hand, and the 
fpinous upon the other-, from the latter they are known, 
becaufe, though they have apertures correfponding to 
gills, they univerfally want the bony apcrcula which co- 
vers them ft. 
Thefe apertures by which they breathe, are placed al- 
ways near the head, but have not uniformly the fame po- 
fition : In fome they are placed beneath, as in the rays, 
and other flat fifth ; in others on the fides, as among the 
fhark 
* He has termed them amphibia nautes. Vide Syftems Natiur®. 
f Willough. Icthyol. 
Pennant’s Brit, Z-ool. Clafs iv. Div. ii„ 
