The colour-sense: its origin and development : an essay in comparative psychology / by Grant Allen.

  • Grant Allen
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: The colour-sense: its origin and development : an essay in comparative psychology / by Grant Allen. Source: Wellcome Collection.

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    again, like the bivalve Mollusca, are enclosed for protec- tion in stout shells, and obtain their food by the creation of currents in the surrounding water. A second group, that of the Entozoa, live in the interior of larger animals, often shut off from the access of light, and bathed by the nutritive fluid of their hosts. These, also, apparently find the possession of eyes no benefit to them. Accordingly, animals originally leading a life of either sort here de- scribed—sessile or parasitic—seldom or never acquire the power of vision; while animals originally possessing that power, which afterwards adopt either of these modes of life, usually or invariably lose their eyes, and become degraded in many other ways, in accordance with the Law of Parsimony, whereby all unnecessary organs become gra- dually obsolescent. On the other hand, any animal which has acquired freedom of motion will naturally derive great advantage from any premonition of food or enemies in his neighbour- hood. Such indications will enable him to rush upon the former or to dart away from the latter. There are various modes by which information of the sort may be given, as by those material particles which arouse the sense of smell, or those undulations of the atmospheric or aqueous medium which awaken the sense of hearing; but the waves of mther described in the last chapter form by far the most certain premonition of all approaching or neighbouring objects, and their reactions finally result in the sense of si<Tht. Of course such a sense cannot arise amongst animals which live perpetually in the dark, like the cestoid and ncmatoid worms, the lob-worm, and the common earth-worm, all of whose freer relatives are provided with more or less perfect eyes; and even those animals which originally possessed visual organs lose them partially or entirely under like circumstances, as we see in the Bopy- rid?e, Acarina, and many other parasites, the blind moles, and tlie well-known sightless fish and reptiles of the Ken- tucky and Carinthian caverns. Similarly, most very deep-