304 OBSERVATIONS ON THE 
slender shaft fringed on the sides with exceedingly 
fine hairs gradually diminishing in length as they 
approach its extremity, which is provided on its 
inferior surface with a profusion of hair-like papillz 
forming a dense brush, and giving the part that 
dilated appearance already alluded to. This struc- 
ture, somewhat modified, as far as my researches 
extend, is common to the tarsal appendages of those 
spiders which are able to ascend the perpendicular 
sides of smooth bodies without supervenient aid; and 
the minute papilla with which the tarsal cushions of 
many insects remarkable for their ability to walk up 
glass are furnished, appear to possess an organization 
closely analogous. 
The hold upon objects which the hair-like papille 
give to the spiders provided with them, depending, 
in a great measure, on the numerous points of 
contact they present, seems to be mechanical ; 
nevertheless, it has been shown by experiment (see 
pp- 222 & 223) that their efficiency in this respect 
must be attributed, principally, to a viscous secretion 
which they emit. At a moderate estimate, there are 
on the appendages which form the brushes occurring 
on the inferior part of the metatarsi and tarsi and 
the digital joint of the pediform palpi of adult 
females of the species Mygale avicularia more than 
4,000,000 papillze of extreme delicacy, a large pro- 
portion of which can be applied by the spider to 
bodies with plain surfaces. If the finger be drawn 
