340 
Transactions of the 
TMonthly Microscopical 
L Journal, June 1, 1869. 
responded exactly witli that between the teeth ; I have frequently- 
used raw meat as food for my flies and have found it eaten freely, 
notwithstanding it has been dried up by being left for some time ; 
they are also able to perforate hard sugar with the help of these 
and the copious supply of saliva with which the whole disc is 
supplied. 
With a view to obtain more perfect specimens of grooved sugar 
I tried, among other materials, the gum paste of the confectioners, 
a mixture of white sugar, gum-tragacanth, and starch. This com- 
position was greedily devoured by the flies, but instead of retaining 
the tool marks better, proved even more soluble than pure hard 
sugar. Probably sugar adulterated with plaster of Paris would 
prove a more suitable material for these experiments. 
Kespecting the teeth of Musca domestica, Captain Lang 
remarks " that there appears to be only one row, each tooth con- 
siderably broader than in Musca vomitoria and tridentate, and 
on either side of these principal teeth may be seen a very delicate 
one, so that there are the same number as in the Blow-fly, though 
differently arranged." I have not yet been able to confirm this 
statement by actual observation, owing to specimens not having 
been procurable. A comparison of the oral appendages of several 
species would no doubt elicit many facts of interest. 
The skeleton of the pseudo-tracheae consists of curiously forked 
half-hoops of chitine (Plate XVI., Fig. 3), correctly figured by Mr. 
Gr. Hunt ; * each piece terminating in a single point at one extremity 
and a fork at the other, so arranged that the row presents an alter- 
nate series of forked and pointed ends ; this supports a membrane 
which follows the zigzag line caused by the forked arrangement, 
each hollow being met by a corresponding projection on the oppo- 
site side, possibly giving the fly the power of accurately closing the 
slit on the upper side of the pseudo-tracheae at will. I do not 
think this view at all inconsistent when it is considered what a very 
mobile organ the whole of the disc is — capable of adapting itself 
closely to the irregularities of any surface with which it may come 
in contact. In the larger main channels before mentioned the forked 
terminations (Plate XVI., Fig. 1) are wanting, and the chitinous 
semi-hoops are divided at the back, probably to give flexibility. 
The arrangement of the chitinous bands near the junctions of the 
various parts of the system is extremely curious, and devised so as 
to allow of the greatest possible amount of motion, consistent with 
the tube being kept open, being given to all the parts (Plate XVI., 
Fig. 2). 
The pseudo-tracheae apparently terminate in tapering ends. 
Whether this is their actual termination I have not been able to 
ascertain. Each pseudo-trachea is accompanied on each side by a 
* ' Microscopical Quarterly Journal,' 1856, p. 238. 
