Fig. 223.—Brain of Perch, side view.
Fig. 224.—Brain of Perch, from above.
If you take the eyeball for comparison, is the whole brain as large as one eyeball? (Fig. [222].) If you judge from the size of the parts of the brain, which is more important with the fish, thinking or perception? Which is the most important sense?
The scales along a certain line on each side of the fish, called the lateral line, are perforated over a series of lateral line sense organs, supposed to be the chief organs of touch (see Fig. [209]).
Fig. 225.—The Stickleback. Instead of depositing the eggs on the bottom, it makes a nest of water plants—the only fish that does so—and bravely defends it.
Questions.—Which of the fins of the fish have a use which corresponds to the keel of a boat? The rudder? A paddle for sculling? An oar? State several reasons why the head of the fish must be very large, although the brain is very small. Does all the blood go to the gills just after leaving the heart?
Fig. 226.—Artificial Fecundation. The egg cells and sperm-cells are pressed out into a pan of water.