Vinegar-fly (Drosophila funebris). 293 
ventral in the pupa of the holly-fly. A bladder-like swelling 
on the head of the fly, also a common feature in Muscidae, 
forces off this id, This bladder may also assist the newly- 
emerged fly to work its way to the surface of the ground 
by helping to displace the particles of earth in its way. 
When newly emerged the fly is of a light-yellowish 
colour, the eyes are bright scarlet, and the wings crumpled 
into small blackish masses. The wings gradually expand 
by blood-pressure, the fly meanwhile running to and fro. 
The fully-developed fly is a small brownish insect about 
one-fifth of an inch in length. The dorsal surface of the 
abdomen is marked by transverse bands of light and 
dark blackish-brown. These bands are more distinct in 
Fie. 10. 
Side view of the fly (female), (x 12.) 
the female because the abdomen is distended with eggs 
(fig. 10). 
Drosophila has a very distinctive flight. It flies very 
slowly and deliberately, changing its course every now 
and then by sudden jerks. When attracted by a fruit 
culture it flies aimlessly to and fro above the fruit for a 
time; then, as if it had just made up its mind, it suddenly 
alights in a very clumsy and abrupt fashion. It is very 
nimble on its legs, running about the surface of the food 
to look for the best feeding or egg-laying sites. 
The head of the Drosophila fly is very similar to that 
of the blow-fly in general structure;* the compound 
eyes, however, are bright red in colour. The bristle of 
the antenna is feathered completely on the upper-side, 
but only the distal half on the lower. The proboscis is 
* Lowne (1890-95), pp. 119-126. 
