

- muscular leaves (7), which thus present 
A CHAPTER ON FLIES. 639 
(m) are comparatively useless, being very short and small, 
compared with the lancet-like jaws of the mosquito or 
horse-fly. But the structure of the tongue itself (labium, 7) 
is most curious. When the fly settles upon a lump of sugar 
or other sweet object, it unbends its Fig. 1. 
tongue, extends it, and the broad knob- i 
like end divides into two broad, flat, 
a sucker-like surface, with which the 
fly laps up liquid sweets. These two 
leaves are supported upon a framework 
of tracheal tubes, which act as a set of 
springs to open and shut the muscular 
leaves. This framework of tracheæ 
does not seem to have been noticed 
in the books at hand while writing, Mr. Edward Bicknell 
having first called my attention to it. He has mounted 
specimens, previously treated with potash, for the micros- 
cope, in his unequalled style, which illustrate admirably the 
structure of the end of the proboscis. In the cut given 
above, Mr. Emerton has faithfully represented these modi- 
fied tracheæ, which end in hairs projecting externally. Thus 
the inside of this broad fleshy expansion is rough like a 
rasp, and as Newport states, “is éasily employed by the 
insect in scraping or tearing delicate surfaces. It is by 
means of this curious structure that the busy house-fly occa- 
sions much mischief to the covers of our books, by scraping 
off the albuminous polish, and leaving tracings of its depreda- 
tions in the soiled and spotted appearance which it occasions 
on them. It is by means of these also that it teases us in 
the heat of summer, when it alights on the hand or face to 
sip the perspiration as it didos from, and is condensed 
Upon, the skin.” 
Every one notices that house-flies are bask abundant 
around- barns in August and September, and it is in the 
ordure of stables that the early stages of this insect are 

