Experiments on Vision. 
245 
at it. The grasshopper threw him off and hopped five inches 
away where it stood still. He at once ran toward it, jumped 
at it and caught it. 
A gnat often brought destruction upon itself by flying across 
the box, although it immediately settled and became quiet, as 
the motion would attract the spiders at any distance up to four¬ 
teen inches. A spider having once caught sight of a gnat had no 
difficulty in finding and capturing it after it had ceased to move. 
One of our little ant-like species, Synemosyna formica, seems 
to have the weakest vision of the whole family. A male of this 
species saw flies in motion four inches away, but if they were 
quiet did'not show that he noticed them further off than one 
and one-half inches. They never eat any but living creatures, 
but they often seem to be deceived by dead flies and gnats, 
leaping upon them when one-quarter of an inch away, and then 
relinquishing them. 
By far the most interesting experiments on vision, however, 
are those that have to do with Attidse in their mating season. 
Here we have evidence that spiders not only see, but see clearly 
at considerable distances. 
Thus we had a male of Saitis pulex, which we put into a box 
containing a female of the same species. The female was stand¬ 
ing perfectly motionless, twelve inches away, and three and a 
half inches higher than the male. He perceived her at once, 
lifting his head with an alert and excited expression, and went 
bounding toward her. This he would not have done if he had 
not recognized her as a spider of his own species. When four 
and one-half inches from her he began the regular display of 
this species, which consists of a peculiar dance. This he would 
not have done had he not recognized her sex. A male of this 
species, on the floor of the box, caught sight of a motionless 
female on the glass, nine inches away and four and one-half inches 
above him. He raised his body almost vertically and gazed al¬ 
ternately at her and at a male, which was five inches away in 
another direction. At other times the males recognized the 
females at eight, nine and eleven inches, and the females recog¬ 
nized the males at six, seven, nine and one-half and eleven 
inches. 
