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Even those among the Amblyopsidae which live in the open have the tropisms of the cave dweller. But these latter are not blind, and the argument only tends to show that the blind fish Amblyopsis entered the caves before it was blind. Nocturnal animals generally must be said to be negatively heliotropic, but these usually have larger and more sensitive eyes than the diurnal.
So a tree is functionally useless, and cannot even exist without a proper supply of light and air; but, whereas it has been the custom to ascribe the heliotropic and other motions to the direct influence of those agents, I would rather suggest that the movements are to some extent due to the desire of the plant to acquire its necessaries of life." The more I have reflected upon Mr.
Loeb states, on the authority of Eigenmann, that all those forms which live in caves were adapted to life in the dark before they entered the cave, because they are all negatively heliotropic and positively stereotropic, and with these tropisms would be forced to enter a cave whenever they were put at the entrance.
He, too, refuses, as usual, to postulate “vital force.” Yet to speak of “the fundamental peculiarities of the living matter inherent in the organism” and to admit that plants are “irritable,” “heliotropic,” “geotropic,” &c., amounts to much the same thing as postulating vital force; that is to say, to a mere naming of the specific problem of life without explaining it.
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