DISEASES OF INSECTS, 203 
not cover the margins of the segments, which gives it 
the appearance of white bands; so that deceived by it, I 
have often at first flattered myself that I had met with 
some new species. ‘The under-side of the abdomen is 
wholly covered by it, divided in the middle into two lon- 
gitudinal masses, the anal segment being bare. De Geer 
has noticed this or a similar disease, which, when flies are 
attacked by it, causes the abdomen to swell so as even 
to burst, and the segments become dislocated. Upon 
opening the abdomen it is found filled with a white unc~ 
tuous substance, which often accumulates (as above de- 
scribed) on its: external surface?. Dr. Host says that 
in this disease when the animal is dead, the wings, which 
were before incumbent, become extended, and its almost 
invisible pubescence grows into long hairs’. De Geer 
seems to think that these flies are thus affected in conse- 
quence of having eaten some poisonous food‘; but I ra- 
ther suspect, as I have observed it become prevalent 
chiefly in wet seasons, that it arises from a superabun- 
dance of the nutritive fluid, or of the fat, so that it seems 
to be a kind of plethora. 
Mr. Sheppard once brought me a panicle of grass, the 
glumes of which were rough with hairs, or small bristles, 
to which several specimens of a fly related to Humerus 
pipiens Meig. adhered by their proboscis. At first I 
thought that having been entrapped by the bristles, and un- 
able to extricate themselves, they had perished from want 
of food; but since when touched they readily dropped 
from the glumes, some other cause, perhaps disease, pro- 
bably occasioned this singular suspension of themselves. 
* De Geer vi. 75. Latr. Hist. Nat. xiv. 371. 
> Jacquin Collectan, i. t. xxi. f. 7. © De Geer whit supr. 
