302 OBSERVATIONS ON THE 
panes of window-glass in any direction whatever, 
unsupported by a single filament, may be easily con- 
firmed by experiment. Among the British Spiders 
observed to ascend with facility well-cleansed win- 
dows and the sides of glass jars in which they have 
been confined, I may name Cludiona accentuata, 
Drassus nitens, Hecaérge spinimana, Philodromus 
dispar, and Salticus scenicus. The last species is ex- 
tensively 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 themselves in opposition to gra- 
vity, I perceived that the tarsi are provided on the 
underside with numerous appendages curving down- 
wards, which are slender at their base and dilated to- 
wards their extremity (see Plate I. fig. 4). 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 vari- 
ous stages of growth, I found that the larger indivi- 
duals experienced greater difficulty in ascending glass 
than the smaller ones, which, in numerous instances, 
