378 PSYCHE. 
intima. Is it not possible that tracheal 
pressure may distend these cells like blad- 
ders, and thus facilitate the aeration of the 
The conditions for their disten- 
tion seem to be present at every pulsation, 
tissues ? 
though under dissection they are always 
I have found such terminal 
enlargements of the tracheae numerously 
developed in the disti-proboscis of the 
house-fly. On one occasion I got a fly 
in a live-cage with the tip of its pro- 
collapsed. 
boscis pressing the cover-glass; and by 
focussing the microscope on this, I found 
that with every pulsation there was a cir- 
cle of flashing lights along the margin 
of the proboscis, as if air was rhythmi- 
cally injected into such sacs. It is easy 
to understand how such distension would 
promote the function of the tracheae as 
carriers of gases between the tissues and 
the outer world. 
Princeton, 24 Nov. 1882. 
CLUSTER-FLIES. 
BY BENJAMIN PICKMAN MANN, WASHINGTON, D. C. 
At a meeting of the Biological society 
of Washington, held 13 Oct. 1882, Mr. 
W: H. Dall exhibited specimens of flies 
which had been sent him from New York 
state with an account of their habit of con- 
gregating in large numbers in unused apart- 
ments of houses, under table-cloths, in pil- 
low-cases, and wherever similar snug places 
of concealment could be found. These flies 
were found from late fall until late spring 
in such situations, but during the summer 
they disappeared. Specimens were put into 
the hands of Dr. C: V. Riley, who made a 
communication upon them at the meeting 
of the same society, 10 Nov. 1882, dwel- 
ling upon the difficulty of identifying the 
species of the fly and stating that it was 
the Pollenia rudis, described by T. W: 
Harris as Musca familiaris, and making 
further remarks upon the synonymy. At 
this meeting Mr. Dall read a letter, received 
since the presentation of his first commu- 
nication, from the parties who had sent the 
specimens, giving a highly colored account 
of the actions of the flies. Dr. Frank 
Baker made a more rational statement in 
regard to the occurrence of flies in Maine, 
which were probably of the same species, — 
and had similar habits. Dr. Baker stated 
that as many of the people in Maine still 
kept up the custom of the home-production 
of yarns and spun goods, and these goods, 
of loose texture, retained upon them a 
considerable quantity of their natural 
grease, the flies were in the habit of bur- 
rowing into such goods, to feed on the 
grease, and were supposed to cut the fibress 
Dr. Riley did not seem to credit the flies 
with this habit, but there seems to be no 
reason to doubt the possibility of such in- 
jury, and not much improbability about it. 
The flies were stated to attach themselves 
sometimes in clusters suspended from ceil- 
ings and other supports, and were on this 
account called ‘‘cluster-flies.” Mr. Dall’s 
informant stated that the flies were proof, 
at least to a great extent, against the influ- 
ence of pyrethrum powder, but Dr. Baker 
said that if the powder was diffused in an 
apartment, and the flies were then caused 
to bestir themselves, and to fly about, they 
succumbed to the influence of the powder 
as readily as other flies. Such a difference 
in observations is not surprising, for it may 
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