488 Mr. BLACKWALL on the Pulvilli of Insects. 
presumptuous ; nevertheless, as facts absolutely irreconcileable 
with this supposition have been forced upon my attention, while 
engaged in examining the evidence by which it is supported, T 
shall, with every sentiment of respect for the high authorities 
to whom I stand opposed, submit my views to the consideration 
of candid and intelligent naturalists. 
Concerning the structure of the instruments by means of 
which flies ascend the vertical sides of smooth bodies, various 
opinions have been promulgated. Some authors compare them 
to sponges, and conjecture that they are designed to contain a 
glutinous secretion capable of adhering to well cleaned glass. 
Dr. Hooke describes them as palms or soles beset underneath 
with small bristles or tenters, like the wire teeth of a card for 
working wool, which he conceived give them a strong hold upon 
objects having irregular, or yielding surfaces; and he imagined 
that there is upon glass a kind of smoky substance penetrable 
by the points of these bristles*. According to the observations 
of Sir Everard Home, they are expanded membranes, having 
their inferior surface granulated, and their edges beautifully 
serrated}; while Messrs. Kirby and Spence, on the contrary, 
remark that they are downy on the underside and granulated 
aboveil. 3 9b | 
_ The want of accordance so conspicuous in the preceding ac- 
counts induced me to inspect the parts minutely under a good 
compound microscope, when it was immediately perceived that 
the function ascribed to them by Dr. Derham and Sir E. Home 
is quite incompatible with their organization. Minute hairs, 
very closely set and directed downward, so completely cover the 
inferior surface of the expanded membranes, improperly deno- 
* Micrographia,p. 170—171. 
+ Transactions of the Royal Society for 1816, p. 323. 
I Introduction to Entomology, vol. ii., Letter X XIII. 
minated 
