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 Saliicus 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 oflBce 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 smaller 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 diflSculty was con- 

 siderably 



