342 
Transactions, &c. 
t Monthly Microscopical 
Journal, June 1, 1S69. 
I consider tlie pseudo-tracheae as channels for the conveyance of 
fluid ; the disc itself I regard as a very perfect sucker. It is evi- 
dent that unless some provision were made by means of these 
pseudo-tracheal channels, either the adhesive power of the surface of 
the disc would be impaired, or else the passage of fluid nutriment 
from the margin of the disc to the centre would be stopped ; the 
open gutters allow of a perfectly free passage for fluids, while the 
membranous interspaces act as suckers. My observations upon 
the living fly feeding upon syrup dried on the cover of a live-box 
have not been very successful, the view being obscured as soon as 
the clear surface of the sugar was roughened by the action of the 
lips, the only fact established being that the lips are capable of 
being closely applied to the surface with which they may be in 
contact ; the state of the pseudo-tracheae whether the slits are open 
or closed, and the action of the teeth and parts about the mouth, is 
still unknown to me, so far as actual observations of the surface of 
the disc are concerned. I have learned far more from watching a 
fly feeding in a cell. 
During the preparation of the present paper I have received 
much valuable information and assistance from Captain Lang and 
Mr. Tatem, of Keading, who have kindly placed their papers and 
specimens at my disposal ; also from Mr. Lowne, to whom I am 
indebted for the names of the various parts of the skeleton, besides 
other help in observations connected with the subject. To these 
gentlemen I tender my thanks, and hope that I may have an oppor- 
tunity of returning their kindness by assisting in their observations 
still in progress. 
I cannot close this paper without calling attention to the great 
value of the binocular microscope for this class of observations ; 
indeed, the introduction of the binocular principle, by revolutioniz- 
ing the mode of preparation, and encouraging the examination of 
thick specimens, with other and better modes of illumination than 
the old way by transmitted light, has been one of the causes of the 
great progress recently made in low-power observations. It is true 
that most of the structures here described can be seen in the old 
preparations, and can be understood by any one who has investigated 
the subject, and examined living specimens, just as a very dilapi- 
dated fossil can be recognized and described by an expert palaeon- 
tologist. Extreme compression is doubtless of service in many, 
instances, but accurate views respecting the arrangement and 
position of parts are only to be formed by, in the first instance, 
examining objects as little removed as possible from their natural 
condition. 
