TO POLISHED VERTICAL SURFACES. 223 
the instruments employed in climbing. The next 
point to be determined, therefore, was, whether 
spiders and insects in the larva and imago states, 
when moving in a vertical direction on clean glass, 
leave any visible track behind them or not. Careful 
and repeated examinations, made with lenses of mode- 
rately high magnifying-powers, in a strong light and 
at a favourable angle, speedily convinced me that my 
conjecture was well founded, as I never failed to 
discover unequivocal evidence of its truth; though, in 
the case of the spiders, considerable difficulties pre- 
sented themselves in consequence of the exceedingly 
minute quantity of adhesive matter emitted by the 
brushes of those animals. On submitting this secre- 
tion to the direct rays of the sun in the month of 
July, and to brisk currents of air whose drying power 
was great, I ascertained that it did not suffer any 
perceptible diminution by evaporation under those 
circumstances. 
Now it is reasonable to infer from the foregoing 
researches that the hair-like appendages constituting 
the brushes of spiders, and occurring in such profu- 
sion on the inferior surface of the pulvilli of insects, 
are tubular. The delicate membrane also on the 
underside of the prolegs, and the tarsi of the perfect 
legs of various larvee capable of traversing polished 
perpendicular bodies without the aid of lines pro- 
duced by a spinning-apparatus, must be provided 
with numerous pores or minute papill, from which 
