34 THE CONDOR Vol. XXI 
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were used for these experiments died several days later, apparently from loss of 
blood. 
During the eleven weeks over which this investigation extended, the mag- 
eots and the resulting flies, since identified as the larvae and adults of Proto- 
calliphora azurea (Fallen) by Mr. C. W. Johnson, curator of the Boston Society 
of Natural History, were studied carefully. These larvae were kept in paste- 
board boxes, in some of which soft cotton or bird nest material was placed. They 
crawled about vigorously until they reached a dark place, the crevices between 
the layers of paper of the boxes being their favorite resting place. 
In these pasteboard boxes various organic substances were placed, such as 
fruit, bread, meat, and boiled potato. Although the fly larvae crawled through 
some of these substances, they fed upon none of them. One day I secured a 
large bone containing many blood cavities. Among these blood cavities I bored 
several holes with my penknife and placed the bone in a box containing several 
dozen fly larvae. The latter had been starved for about a week so that there 
was not the shghtest trace of food left in their intestines. The next morning 1 
found two or three of them with fresh traces of blood in their alimentary canals, 
conclusive evidence that they had been feeding upon the ox blood contained in 
the bone. One day, having accidentally cut myself, I put several drops of blood 
in the palm of my hand and placed several larvae near it, but the latter invari- 
ably crawled in the opposite direction as soon as they came in contact with the 
blood. Similar experiments with ox blood brought the same results. This seems 
to indicate that the larvae require a firm object to which they can attach them- 
selves before they make any attempt to ingest blood. 
Larvae which had not reached their full growth when taken from nests 1n- 
variably died, unless they could feed upon blood. On the other hand full-grown 
larvae always pupated, even if they had no access to food of any kind. This 
shows that the larvae of Protocalliphora azurea are absolutely dependent upon 
blood in order to mature. 
The blood ingested by the larvae is stored in a kind of reservoir, the diverti- 
culum, which branches off from the esophagus close behind the pharynx and 
there retains its red color for three or four days, gradually passing into the 
posterior end of the intestine as a dark brown substance which appears as a 
longitudinal streak in the middle of the animal’s body. If the larvae are not fed, 
this streak is gradually discharged as faeces so that after five to seven days 
more, the larvae become creamy white in color throughout. From this we may 
infer that it is not necessary for the larvae to replenish their supply of food at 
frequent intervals to attain full growth. 
When the larvae are about to pupate, they crawl, anterior end downnenel 
into the sticky mass at the bottom of the nest and there sometimes form a kind af 
disk, the lower side of which is made up of the anterior ends of the larvae, and 
the upper side of the posterior ends. About two weeks after pupation, the young 
flies emerge from the lower side of the disk. The whole thing reminds one some- 
what of the state of affairs in wasp nests. Here too the young wasps emerge 
from the lower side of the disks. In captivity the fly larvae, before they pupate, 
usually attach themselves to objects located in dark places by means of a viscous 
fluid which solidifies a few moments after it has been discharged. 
One thing which surprised me very much was the power of resistance hich 
these larvae showed. Several of them, after having been immersed in a 70 per- 
cent alcohol solution for twenty-four hours, were still wriggling vigorously. Sev- 
