_Laboratory exercise._--Study of a living fish--adaptations
for protection, locomotion, food getting, etc.
_Laboratory demonstration._--The development of the fish or
frog egg.
_Visit to the aquarium._--Study of adaptations, economic
uses of fishes, artificial propagation of fishes.
Two Methods of Breathing in Vertebrates.--Vertebrate animals have at least
two methods of getting their oxygen. In other respects their life processes
are nearly similar. Of all vertebrates fishes are the only ones fitted to
breathe all their lives under water. Other vertebrates are provided with
lungs and take their oxygen directly from the air.[32] We will next take up
the study of a fish to see how it is fitted for its life in the water.
Footnote 32: With the exception of a few lungless
salamanders. Most salamanders get much of their supply of
oxygen through their moist skins.