234 
PecJcham—The Sense of Sight in Spiders. 
shorter distance that Epiblemum sees its victim clearly enough 
to capture it. In other instances the spiders paid no attention 
to living flies which were not in motion, although passing at a 
distance of four centimeters. 
M. Plateau remarks that the distance of two centimeters is 
not chosen because it is the limit of the spider’s leaping pow¬ 
ers, as it is able to jump twice as far. 
Of Marpissa mucosa he says that at four centimeters the spi¬ 
der perceives the movements of a fly, but that it is only the 
movements that are noticed, since at this distance, and even at 
three centimeters, it seems to lose sight of its prey and to re¬ 
lapse into complete indifference if the fly becomes perfectly 
motionless. 
It seems to us that these experiments and a number of sim¬ 
ilar ones performed by Plateau, show not how far the spider 
can see distinctly, but at what distance it usually seizes its 
prey. It is not safe to take for granted that if the spider does 
not try to catch the fly he therefore does not see it. As a mat¬ 
ter of fact spiders will often let flies—which certainly are, 
as M. Porel has said, both stupid and imprudent—not only 
come within two centimeters of them, but climb upon them and 
walk all over them, practically putting their heads into the 
lion’s mouth, and yet will seem unconscious of their existence. 
Perhaps they are not hungry. At any rate such are the facts. 
Dr. McCook says, “One of our largest indigenous Laterigrades, 
the Huntsman Spider (Herterapoda venatoria), received from 
Florida and kept in captivity, permitted a large fly placed in 
her cell to run between the legs, fly into the face, alight on 
the back, without any attempt to capture it. In the course of 
time, however, the fly lit on the side of the box a short dis¬ 
tance in advance of the Huntsman. She perceived it, crouched, 
slowly moved her limbs, stealthily and by almost inperceptible 
advances approached, then swiftly shot forth her claws and se¬ 
cured her victim. 8 
M. Plateau tried another set of experiments with the same 
spiders in which all the conditions were the same except that 
instead of a fly he used three rude imitations of that insect, 
Ibid, p. 286. 
