STRUCTURE AND ECONOMY OF SPIDERS. 303 
were capable of moving on an ordinary window-pane, 
even in an inverted position, or with the back down- 
wards. It was evident also that physical energy 
(other conditions being the same) gave its possessor a 
decided advantage in this respect. When highly 
polished glass of a superior quality was employed, the 
difficulty was somewhat increased ; and, in all cases, 
those spiders effected an ascent with the greatest 
effort which, in proportion to their bulk, had the in- 
ferior surface of their tarsi most sparingly furnished 
with the requisite apparatus. These results, some 
of which are in direct opposition to the hypothesis 
I had previously entertained, determined me to in- 
spect the tarsal appendages more minutely than I 
had hitherto done; and a peculiarly favourable 
opportunity umexpectedly presented itself. Three 
living specimens of Mygale avicularia having been 
brought accidentally to Manchester, in dye-woods 
imported from the West-India Islands during the 
year 1830, I availed myself of the circumstance to 
examine under the microscope the appendages with 
which the tarsi of that gigantic species are so abun- 
dantly 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 dis- 
appointed ; and I shall now proceed to describe the 
organization of the appendages, which is much more 
complex than I had anticipated. Each consists of a 
