Page:First course in biology (IA firstcourseinbio00bailrich).pdf/355

front of the optic lobes lie the two cerebral lobes, or the cerebrum. The small olfactory lobes are seen (Fig. 224) in front of the cerebrum. The olfactory nerves may be traced to the nostrils. Back of the optic lobes (mid brain) is the cerebellum (hind brain), and back of it is the medulla oblongata, or beginning of the spinal cord.

Fig. 223.—Brain of Perch, side view.

Fig. 224.—Brain of Perch, from below.

Taking the eyeball for comparison, is the whole brain as large as one eyeball? (Fig. 222.) Judging 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