176 
ANIMAL ACTIVITIES. 
with the gullet. This bladder serves to vary the 
specific gravity of the fish in the water. Sometimes it 
is used in producing a noise. It is homologous with 
the lungs of higher vertebrates. 
The heart in fishes consists of one ventricle and one 
auricle. Impure blood, collected by the veins, gathers 
in the auricle and passes to the ventricle, whence it is 
forced through the gills where the ordinary interchange 
of gases takes place. The blood is then distributed to 
all parts of the body by arteries. See Fig. 132. 
Questions. What do you mean by saying that a fish 
is cold-blooded ? 
How much can a fish see ? 
How much can it hear ? 
What is meant by saying that a fish’s ears are 
probably organs of equilibrium ? 
Where are organs of equilibrium situated in some 
other animals ? 
How does the tail of a shark differ from that of a 
salmon ? 
How do the skeletons of the two animals differ ? 
Topics for Reports. The Nests of the Stickleback. 
The Migrations of Salmon. Bream. Trout. Sharks. 
Electric Eels. The Sea-serpent. Flying Fish. 
VOCABULARY. 
A or'ta (Gr. aeiro , to raise), the 
large artery of the body. 
Ar'te ry (Gr. arteria , windpipe), 
a tube carrying blood away 
from the heart. 
Cau'dal (Lat. cauda, tail), pertain¬ 
ing to a tail. 
Cen'trum (Lat. centrum , a centre), 
the body of a vertebra. 
Cerebel'lum (Lat. dim. of cere¬ 
brum ), the hind brain. It con¬ 
trols combined muscular action. 
Cer'e brum (Lat. cerebrum, brain), 
the front brain, the seat of the 
reasoning faculties. 
Chor da'ta (Gr. chorde , a chord). 
The sub-kingdom including the 
back-boned animals. 
Hae'mal (Gr. haima , blood), per¬ 
taining to the blood. Sometimes 
used with the same meaning as 
visceral. 
Het er 0 cer'cal (Gr. heteros , differ¬ 
ent, and kerkos , tail), applied to 
the tails of fishes having unequal 
lobes. 
Ho mo cer'cal (Gr. homos , same, 
and kerkos'), a word applied to 
the tails of fishes having equal 
lobes. 
