318 Mr. A. E. Cameron on the 
fourteen hours of an aquatic life did not trouble it much. 
An all-night sojourn in a weak solution of alcohol consisting 
of water mixed with beer, also failed to disturb its equa- 
nimity ; for it became as active as ever when withdrawn. 
Granted a short rest and allowed some nourishment, the 
larva refreshed, successfully tackled the final test, a day’s 
submersion in undiluted beer. Having emerged with 
flying colours, or, should we say, retaining all its cuticular 
iridescence, it was restored to a diet of decaying beetroot, 
when it shortly afterwards pupated and completed its 
metamorphosis. Such a tenacity of life is not, I should 
imagine, shared by many larvae. 
Tue Pupa. 
After becoming full grown the larva rests for a short 
time previous to pupating, when it undergoes contraction 
from 9 mm. to 5 mm., assuming the barrel shape char- 
acteristic of Muscid pupae. The pupae vary in size, the 
average size being 5 mm. in length by 1:9 mm. broad. 
During the process of pupation, which occupies about a 
couple of hours, the colour changes from a creamy white to 
a reddish brown, and as the development of the imago 
proceeds within, the puparium gradually becomes darker. 
Most of the larval characters are discernible in the pupa; 
but owing to the shrinkage which has occurred, the relative 
position of organs has been affected. The prothoracic, 
lateral spiracles are now situated almost quite at the 
anterior end of the pupa, and two small projections pos- 
teriorly, denote the position of the posterior spiracles. 
Inside the breeding-cages the larvae pupated in the drier 
portions of the cow-dung. 
At the termination of twelve to fourteen days under the 
laboratory conditions employed, the imagines were ready - 
to emerge, and they made their exit from the pupa cases 
by a T-shaped split at the anterior end,—the fly employing 
the ptilimum to push the valves apart. 
Under ordinary natural conditions Farsky states that 
the pupal period of development lasts for three and a half 
to five weeks, and in moist, damp weather it may be even 
more prolonged. It must be always borne in mind that a 
difference in the nature of the food of the larva may be of 
radical importance in determining the length of the period 
occupied by the insect in its metamorphosis, where other 
conditions of temperature and moisture are equal. In 
