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 sparinglj?^ 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 

 T 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. 



Tlie 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-^ 



3 Q 2 tact 



