THE BREATHING APPARATUS, ETC., OF FISH 23 
then divides into 
fine capillaries, in 
which the blood 
is oxygenated and 
returns purified 
into the circulatory 
system. 
ine: uwater 
having supplied the 
gills with oxygen, 
passes out through 
the gill-cover, 
which, in most 
Teleosteous fish, 
takes the form of 
BONES OF HEAD OF THE PERCH. 
(After Giinther.) 
a slit, marking the division between the head and the trunk. 
It is protected by a thin, bony, external plate, called the oper- 
culum (Figs. I. and II., 28), which with other bones, termed, 
Fic. III. 
BONES OF PART OF HEAD OF THE PERCH. 
(After Giinther.) 
from their posi- 
tion relative to 
it, the praoper- 
culum (Jdid., 30), 
the suboperculum 
(Lbid., 32), and the 
interoperculum 
(Jdid., 33), form 
the gill-cover. 
Now the gills 
are very delicate 
organs; a fish 
which may recover 
from frightful 
external injuries 
succumbs to a 
comparatively 
