SKATES. 
79 
divisions or doublings of tbe membrane of the gills. Each 
ision as on each side of it one hundred and sixty sub- 
^visions or folds of its membrane, the length of each of 
and*^ \ ^ of an inch, 
th sixteenth of an inch; so that in 
fold ^ there are one hundred and forty-four thousand 
fou tb which arc equal to. the sixty- 
or h part of a square inch, or the surface of the whole 
inci* to two thousand two hundred and fifty square 
^ 0 les, that is, to more than fifteen square feet, which have 
h^” supposed equal to the whole external surface of the 
co^fo^^ ^ Sood injection by an artificial 
of the artery, a microscope is applied, the 
with ^ .°f ^^0 membrane of the gills is seen covered 
fM ^ ^oautiful network of exceedingly minute vessels. — 
pai”"^°’ ''Structure and Physiology of Fishes,” p. 15.) Those 
t^aiticulars are given the more at length because they belong 
alth “‘I Skates, 
ind°T^i ^ degree. And, 
still 1 * !j ^ applicable to fishes in general, although in a 
the ^S’ree in the class termed the bony fishes, in which 
nianr^^^*^ through the gills in a more rapid 
ler, to make amends for the less extent of surface to 
'^°\oh It IS applied. 
vess 1 brought to this purifying apparatus by a 
poi^-f ^ specially framed to be a 
caiT^* f °f propulsion; for although the general 
prin^' 'i ‘circulation of the blood is formed on the same 
vari ^ fishes, the peculiarity of action and the power 
witir as regards the present genus, compared 
sin 0-1 others. In Sharks and Skates the heart is of ti 
oririn T complex structure, mingled with simplicity; the 
from artery, or vessel which bears the blood 
tube consisting of a long muscular 
itself f"® regarded as an extension of the heart 
a rem^^T iT tends greatly to aid its powers of action; but 
nhv«i r ^ circumstance attending it is the degree of what 
irritability that resides in it, and which 
whirl I'* powers of life and action under circumstances 
to other races mun speedily prove fatal. I have even 
