480 Mr. BLACKWALL on the 
lines emitted from their spinners is so widely extended, that an 
attempt to prove its fallacy in particular cases will, in all proba- 
bility, be received with some distrust: nevertheless, the fact 
that several species have the power of traversing vertical panes 
of window-glass in any direction whatever, unsupported by a 
single filament, may be easily confirmed by experiment. Among 
the British spiders observed to ascend with facility well cleansed 
windows, and the sides of glass jars in which they have been 
confined, I may name Drassus melanogaster and Salticus scenicus. 
The latter species is extensively known, and may be readily 
, procured in warm sunny weather in summer, on the walls of old 
buildings having a southern aspect. 
On examining the legs of these animals under the microscope, 
with a view to discover the means by which they support them- 
selves against gravity, I perceived that the tarsi are provided 
on the underside with numerous appendages curving down- 
wards, which are slender at their bases and dilated towards their 
extremities. The idea immediately occurred to me that these 
appendages may perform the office of suckers, and that the 
spiders are probably enabled to adhere to the upright sides of 
smooth objects by atmospherical pressure; but being sensible 
that mere conjecture, however plausible it may appear, is the 
bane of Natural History, I resolved to investigate the subject 
experimentally. Having obtained spiders of the above-named 
species, in various stages of growth, I found that the larger indi- 
viduals experienced greater difficulty in ascending glass than 
the smal'er ones, which in numerous instances were capable of 
moving slowly on an ordinary window-pane, even in an inverted 
position, or with the back downwards. It was evident also that 
physical strength (other conditions being the same) gave its pos- 
sessor a decided advantage in this respect. When highly polished 
glass of a superior quality was employed, the difficulty was con- 
siderably 
