272 
RESPIRATORY ORGANS OP FISHES. 
fluid, and then forces it through, the apertures on each side of 
the throat, into the gill-cavities; and from these it passes out 
by the other orifices just described. Fishes, in common with 
other animals that breathe by gills, can only respire properly 
Fig. 155.— Lamprey. 
when these are kept moist, and are so spread out as to expose 
their surface to the surrounding element. The act of respira¬ 
tion can take place when they are exposed to air , provided 
these conditions be fulfilled; hut in general it happens that, 
when a Fish is taken out of water, its gills clog together and 
dry up, so that the air cannot exert any action upon them; 
and the Fish actually dies of suffocation, under the very cir¬ 
cumstances which are necessary to the life of an air-breathing 
animal. 
318. There are certain Fishes, however, which are provided 
with an apparatus for keeping the gills moist, somewhat re¬ 
sembling that which has been already noticed in the land- 
crab. The bones of the pharynx are extended and twisted 
in such a remarkable 
manner (fig. 156), as 
to form a number of 
small cavities; these 
cavities the Fish can 
fill with water; and 
they form a reservoir 
of fluid, from which 
the gills may be sup¬ 
plied with a sufficient 
amount to keep them 
moist during some 
time. The gill-fila¬ 
ments themselves are 
so arranged that they do not clog together; and by this combi¬ 
nation of contrivances, the species of Fish that are furnished 
with it can live for a long time out of water, so as to be able to 
journey for a considerable distance on land. Such a provision 
Fig. 156. —Respiratory Apparatus of Anabas. 
