Results of Observations. 
233 
exactly described procedure with an exactly described animal 
can always be repeated, by which means our interpretation, if 
it is due to variable bye-conditions, is at once corrected, and at 
all events thoroughly cleared from the influence of personal pre¬ 
conception, which has so great a share in so-called self-observ- 
vation. ” 7 
In 1887 Prof. Felix Plateau brought out a paper upon the 
sense of sight in Arthropods, and by 1888 he had published four 
more papers, covering the whole field of Arthropod vision. In 
the second of these papers he treats of the sight of spiders. 
M. Plateau is in accord with naturalists generally in the 
opinion that the question of the range of vision in insects is 
only to be determined by observation, and that, so far, mor¬ 
phology has been of but little use in solving the problem. He 
has, himself, followed the experimental method, but in working 
over so large a field as the Arthropoda he has very naturally 
drawn some conclusions that a more intimate acquaintance with 
the creatures in his hands would have taught him to avoid. 
Thus he states, after experimenting with a small number 
(five), of species, that the sight of two large groups of spiders, 
the Attidse and the Lycosidse, is very bad, the limit of clear 
vision being about one or two centimeters. 
The observations upon which he bases this conclusion were 
different for the two groups. In studying the Lycosidse he took 
from two females the cocoons which contained their eggs, and 
noted that although they sought for them eagerly they did not 
find them until they came very close. These experiments will 
be considered further on. 
For Dolomedes fimbriatus and for two Attidse, M. Plateau 
pursued a different plan. He first noted, in numerous instances, 
that both free and captive spiders did not leap upon a fly 
until it came as near as two centimeters. 
He found that Epiblemum scenicum turned from side to side 
to follow with its eyes the movements of a fly ten and twelve 
centimeters away, and that it ran after the fly from a distance 
of five centimeters; but this, he says, signifies only perception 
of movement and not perception of form, since it is at a much 
7 History of Materialism, Yol. Ill, p. 178. 
