L'Urr to the burgeon (intend oj the Army accompany ing seven photographs of the proboscides of 
certain Jiies. 
BRIGADIER GENERAL J. Iv. BARNES, 
Army Medical Museum, 
January 15, 1872. 
Surgeon General, I’. S. Army. 
General: The series of negatives of microscopic views of parts of insects, made by me during the 
last Christmas hulidays, under the circumstances related in iny letter accompanying the photographs of the 
Mosquito, embraces several views of the proboscides of certain flies, copies of which I transmit herewith, 
with the following explanatory remarks. 
The head of the common house fly, and of many other flies, bears, anteriorly, connected with its under 
surface a flexible, fleshy, trunk-like, proboscis or sucking apparatus, by means of which the insect absorbs its 
liquid food. Accounts of the structure of this organ are to be found in many entomological treatises, but 
perhaps the most satisfactory is that given by Mr. B. T. Lownes in his monograph of ‘-The Anatomy and 
Physiology of the Blow-fly,” (London, 1S70.) 
Mr. Lownes justly declares the proboscis of this fly to be -‘one of the most remarkable and complex 
structures found in the insect world.” He describes it as consisting of three joints, its hard parts being 
the homologues of those usually found in the mouths of insects, but here greatly modified to fit them for 
their special functions. The basal joint is moved at the pleasure of the insect by five pairs of muscles. 
The walls of this joint are double and capable of being dilated into a cavity by the action of a pair of 
strong muscles. By its alternate dilatation and collapse this organ acts as a pump to draw up the liquids on 
which the insect feeds. The cavity is continuous behind with the oesophagus, and anteriorly with a hollow 
tube in the second segment, which leads to the oral orifice. 
I he terminal joint or segment of the proboscis consists of two large fleshy lobes, which, when at rest, 
are folded together, but when the insect is feeding are opened so as to form an oval sucker divided 
into two parts by a fissure which terminates posteriorly in a triangular orifice or mouth leading directly to 
the sucking tube. These fleshy lobes arc channelled by numerous canals called false tracheae, which arc 
kept open by incomplete rings, and which lead to the sucking tube just above the oral orifice. “These” 
says Mr. Lownes, “form a fine strainer through which the insect is enabled to filter the fluid from the solid 
portion of the substances on which it feeds.” 
hor further particulars Mr Lowness monograph may be consulted. The above sketch will serve to 
give some idea of these curious organs, which are but imperfectly shown in dried specimens such as were 
used for the preparation of the photographs, of which the following is a brief description. 
No. 1. Gives a general view of the Wine-cellar Fly ( Drosophila cellaris ) magnified 1G diameters. 
Negative No. 532, new series. The photograph represents one of these flies carefully flattened out, so that 
the proboscis protrudes from the extremity of the head. It gives an idea of the size of the proboscis as 
compared with the bulk of the insect. 
No. 2. Represents the same proboscis magnified 80 diameters. Negative No. 533, new series. 
No. 3. Represents the same magnified 1&5 diameters. Negative No. 535, new series. Both No. 2 
and No. 3 distinctly show the numerous transversely marked, false tracheae of the sucking lobes, the tube 
of the second joint, and the thick massive first joint, which also has attached to it on each side two curious 
