File:Animal life and intelligence (1895) (18198466421).jpg

Title: Animal life and intelligence
Identifier: animallifeintell00morg (find matches)
Year: 1895 (1890s)
Authors: Morgan, C. Lloyd (Conwy Lloyd), 1852-1936
Subjects: Biology; Animal intelligence; Psychology, Comparative; Evolution
Publisher: Boston, Ginn
Contributing Library: Boston College Libraries
Digitizing Sponsor: Boston Library Consortium Member Libraries

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The Senses of Animals. 291 stippled with the fine stippling of the ends of the rods and cones. In insect-vision the stippling is far coarser, and the image is produced on different principles. In the vertebrate the image is produced by a lens; in the insect's eye, by the elongated cones. How this is effected will be readily seen with the aid of the diagram. At a 6 are a number of trans- parent rods, separated by pigmented material absorb- ent of light. They repre- sent the crystalline cones. At c d is an arrow placed in front of them ; at e f is a screen placed behind ,, t-> n -i • 1 , , , Fig. 38.—Diagram of mosaic vision. them. Eays of light start in all directions from any point, c, of the arrow; but of these only that which passes straight down one of the trans- parent rods reaches the screen. Those which pass obliquely into other rods are absorbed by the pigmented material. Similarly with rays starting from any other point of the arrow. Only those which, in each case, pass straight down one of the rods reach the screen. Thus there is produced a reduced stippled image, c' df, of the arrow. There has been a good deal of discussion as to the relative functions of the ocelli and the facetted eyes of insects. The view generally held is that the ocelli are specially useful in dark places and for near vision ; while the facetted eyes are for more distant sight and for the ascertainment of space-relations. How the two sets of impressions are correlated and co-ordinated in insect-con- sciousness, who can say ? * The interesting observations of Sir John Lubbock seem to show that insects can distinguish between different colours. " Amongst other experiments," he says,f " I * We must remember how largely the antennae are used when an insect is finding its way about. Watch, for example, a wasp as it climbs over your plate. If the antennae be removed, it seems to stumble about blindly. The antennae seem almost to take the place of eyes at close quarters. f " Senses of Animals," p. 194.

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