File:Fishes (1907) (14590804820).jpg

Identifier: fishes00jord (find matches)
Title: Fishes
Year: 1907 (1900s)
Authors: Jordan, David Starr, 1851-1931
Subjects: Fishes
Publisher: New York, H. Holt and Company
Contributing Library: Smithsonian Institution Libraries
Digitizing Sponsor: Smithsonian

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the swim-bladder and the way the fish came to acquire it as a substitutefor a lung. The Brain of the Fish.—The movements of the fish, like thoseof every other complex animal, are directed by a central ner-vous system, of which the principal part is in the head and isknown as the brain. From the eye of the fish a large nervegoes to the brain to report what is in sight. Other nerves gofrom the nostrils, the ears, the skin, and every part which hasany sort of capacity for feeling. These nerves carry their mes-sages inward, and when they reach the brain they may be trans-formed into movement. The brain sends back messages to themuscles, directing them to contract. Their contraction movesthe fins, and the fish is shoved along through the water. Toscare the fish or to attract it to its food or to its mate is aboutthe whole range of the effect that sight or touch has on theanimal. These sensations changed into movement constitutewhat is called reflex action, performance without thinking of
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The Life of the Fish i 3 what is being done. With a boy, many familiar actions may beequally reflex. The boy can also do many other things of hisown accord, that is, by conscious effort. He can choose amonga great many possible actions. But a fish cannot. If he isscared, he must swim away, and he has no way to stop himself.If he is hungry, and most fishes are so all the time, he will springat the bait. If he is thirsty, he will gasp, and there is nothingelse for him to do. In other words, the activities of a fish arenearly all reflex, most of them being suggested and immediatelydirected by the influence of external things. Because itsactions are all reflex the brain is very small, very primitive, andverv simple, nothing more being needed for automatic move-ment. Small as the fishs skull-cavity is, the brain does nothalf fill it. The vacant space about the little brain is filled with a fattyfluid mass looking like white of egg, intended for its protection.Taking the dead sunfish (for t

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