554 
The fet. 
and are extremely deltrudtive to butcher meat, and other 
kinds of proviiion. 
Next to the number of flies, their variety claims our 
attention. The different fpecies are extremely diverfified 
in their external form, their ftrudture, their organization, 
their metamorphofis, their manner of propagating their 
fpecies, and in providing for their pofterity. A full ex- 
planation of thefe different parts of their economy, would 
require a large volume, and would conftitute a narrative 
to many readers not uninterdling. Such an undertaking, 
however, is incompatible with the limits preferibed to 
our work. 
Some of thefe infedls have trunks inftead of a mouth ; 
others have that organ armed with teeth ; and many have 
both a mouth and a trunk. The probofeis of flies is a 
machine contrived for pumping the blood from the vef- 
fels of large animals, and the nedtar from the petula of 
flowers ; and the fcience of hydraulics has not enabled 
men to conftrudt machines more complicated, more ex- 
actly arranged, or better adapted to thefe purpofes. Some 
of them poffefs confiderabie firmnefs and folidity, thofe 
efpecially that are deftined to pierce the Ikir.s of cattle. 
In order to fee them at work, all that is neccffary is to 
expofe a fyrup to attract them, and to take up a lens for 
their infpedtion. 
Each eye of the fly contains in it an affemblage of a 
great number of fmall ones, which probably have the 
effect of multiplying the furrounding objedts, and creating 
reprefentations of them, which the experience of the in- 
fect corredts *. From the eye, if you par's along and fur- 
vey 
• Reaumur, Tome IV, Mem- vk 
