THE ELY. 
535 
Yey the body, you fif'd it provided with the organs of 
refpiration. Four fmall ftigmata, for this purpofe, are 
found upon the thorax, and a greater number difperfed 
over the annuli of the abdonaen. The covering of the 
different parts of the abdomen are fcaly, and do not con- 
fift all of one piece, but admit of the contraaion and di- 
latation of that part, according to the circumdances of 
the animal. Each of the feet terminates in a fmall bunch 
of feta?, refembling a brufh. 
The interior organization of this genus, when examin- 
ed with a proper apparatus, prefents two pulmonary facs 
of a white colour, arranged longitudinally along the body. 
As the bodies of fome fpecies are diaphanous, the aftion 
of the heart may alfo be dtfcerned, as well as the liquor 
it contains, continually driven along the great artery 
leading to it, and returning by the fame courfe*. During 
their larva Hate, the flies in general go through a greater 
variety of metamorphofes than even the filk or butterfly- 
worms : During their progrefs from the vermicular to 
the chryfalis date, they pafs through an intermediate 
change, unexperienced by other infeeds. From the diort- 
nefs of their lives, all thefe viciffitudes mud rapidly fuc- 
ceed each other : this circumftance, however, does not 
prevent many fpecies from condrudinga coque for their 
lad metamorphofis, of a curious fabric. The greater 
part of thefe coques are of filk, with a mixture of other 
materials ; thofe, indeed, mod common with us, ferve 
themfelves with their own lkin, which becomes an in- 
crudated covering to proted them during their dormant 
and aurelia date. 
When 
* lictn, ubi fupr*i 
