The Arizona sentinel., 1888-09-08
SIGHT OF SPIDERS.
Prof. Plateau Claims That It Does Not
 Exceed Q Few Inches.


 Exceed Few Inches.
 Prof. Plateau has been examining the organs of sight among the Arach- nida. Their development in this re- spect is far from uniform. Some, like the scorpions, shun the daylight, and must depend upon chance or upon their other senses for the capture of their prey, Others, like the majority of the true Arachnida, hang out snares for insects, while other families in this group seek the light and live by hunt ing. In these latter the visual percep- tions have reached tase highest grade of development.
 Thanks to the numerous eyes of the spider, it is popularly credited with excellent sight Naturalists, however, have long ago refuted this error, and shown that these eyes, in virtue of their curious dimorpuism dis covered by Grenacher, are very indifferent instruments, or at least that their possessors must be very short-sighted. Muller and Lacordaire find that spiders see dis tinctly only to a very short distance. Duges thinks that if a spider takes ref uge in its hole at the approach of man, even at the distance of fathom, it is not necessary to suppose that it has any distinct vision at such dis tance, but merely recognizes moving masses.
 The researches of NJ. Plateau have not merely confirmed these surmises, but have extended them in an uneX- pected manner. His minute expert ments have been extended to various species of spiders, and have led him to conclude that the distance at which vision is sufficiently distinct to induce a spider to capture its prey is about an inch in the most sharp-sighted species, and that the vague perception of move ments to Epiblemum scenicum does not exceed five or six inches.
 The following observations, which the reader may verify in any garden on fine day in the latter part of sum- mer, fully confirm the statements of M. Plateau. If blue-bottle falls into the web of geometrical spider (Epeira diadema), she does not rush right to the spot, but applies her feet in rapid succession to the radii of the web, and thus ascertains by touch the exact position of the struggling prey. If the web is gently touched with blade of grass or a soft feather she rushes to the attack, and does not at once per ceive the fraud. but actually seizes the useless object.
 We have seen harry-long-legs ssget entangled in a cobweb in his blunder- ing flight, and just manage to extricate himself in time, leaving leg behind him as forfeit. The spider, hurry ing up, seized the leg, not noticing that it was bodyless, ran to the other end and then back to the first, only learning by very close examination that the booty was just a leg and nothing more. No creature having a moderate range of vision could be so deceived.
 The conclusions of M Plateau are that the Arachnida in general perceive the movements Of bulky bodies from distance. The so- called hunting spi- ders, such as the Lycose, are probably the only ones which see the movements of small objects. They perceive such movements within a range, according to some observers, at from one inch to foot, but which, according to Plateau, such small distances their sight is not distinct. Weaving spiders have very poor sight at any distance, and only detect the presence and the position of their prey by the vibrations of the web. Cosmos.