Structure and Economy of Spiders. 481 
siderably increased ; and in all cases, those spiders effected an 
ascent with the greatest effort, which, in proportion to their 
bulk, had the inferior surface of their tarsi most sparingly fur- 
nished with the requisite apparatus. These results, some of 
which are in direct opposition to the hypothesis I had previously 
entertained, determined me to inspect the tarsal appendages 
more minutely than I had hitherto done; and a peculiarly favour- 
able opportunity unexpectedly presented itself. Three living 
specimens of Mygale avicularia having been brought accident- 
ally to Manchester in dye-woods imported from the West India 
Islands during the present year (1830), I availed myself of the 
circumstance to examine under the microscope the appendages 
with which the tarsi of this gigantic species are so abundantly 
supplied; conceiving that their structure would be exhibited to 
greater advantage in a recent subject than in individuals which 
have long occupied a place in the cabinet. In this expectation 
I was not disappointed ; and I shall now proceed to describe the 
organism of the appendages, which is much more complex than 
I had anticipated.— Each consists of a slender bristle fringed on 
the sides with exceedingly fine hairs gradually diminishing in 
length as they approach its extremity, where they occur in such 
profusion as to form a thick brush on its inferior surface, giving 
the part that dilated appearance already alluded to. ‘This 
structure, as far as my researches extend, is common to the tar- 
sal appendages of those spiders which are able to ascend the 
perpendicular sides of smooth bodies without supervenient aid ; 
and the minute bristles with which the tarsal cushions of many 
insects, remarkable for their ability to walk up glass, are fur- 
nished, appear to possess an organization closely analogous. 
The hold upon objects which the setaceous bristles give to the 
spiders provided with them seems to be purely mechanical, 
depending, in a great measure, on the numerous points of con- 
3Q2 tact 
