HABITS OF THE ADULT FLY 
53 
it has been made after a long series of comparative 
studies, and its truth will readily be admitted by any 
one who has paid much attention to the flight of Dip- 
tera. Cobb, in his paper on the Fungous Maladies of 
the Sugar Cane, records a number of observations on 
the flight of flies in connection with the distribution by 
the flies of the spores of a fungous disease of sugar 
cane. He states that he never succeeded in tiring his 
flies very perceptibly if they had a free space to move 
around in. When confined in a room they were kept 
on the wing for hours without showing much fatigue. 
By dissection he showed that with certain of the Sar- 
cophagid flies the thoracic or wing muscles constituted 
twenty-six and two-tenths per cent, of the weight of the 
fly, and that the mass of the great thoracic muscles is 
proportional to the apparent power of flight among dif¬ 
ferent flies. He records also a remarkable example of 
the power of flight of one of the larger flies. On a 
voyage across the Mediterranean from Algiers to Mar¬ 
seilles, he observed a Dipterous insect keeping pace with 
the steamer “so accurately that it almost seemed as 
if it were joined to the boat by some invisible rigid 
connection. The boat left Algiers at noon and as long 
as there was any light left by which to observe, the 
insect kept its place steadily. This was in midsummer. 
The insect never made any attempt to come aboard. 
The boat was not particularly fast, her speed being 
about thirteen knots.” 
Every one who has driven a fast team of horses over 
a road through pine timber must have noticed the ex- 
