368 THE AMERICAN NATURALIST. 
There is a great breaking down of the larval organs of 
Blepharocera. With such a specialized larval life there is a 
great difference between the larval organs and the imaginal 
organs. The musculature, the alimentary canal, and the res- 
piratory system are largely broken down and reformed. And 
in all of this histolysis phagocytes are abundant and conspicu- 
ous. When pupa not more than three or four days old are 
dissected, the body cavity is found to be filled with “pseudo- 
yolk," that is, with a lymph-like liquid containing floating bits 
of degenerating tissue and hosts of phagocytes. A bit of 
larval muscle (Fig. 2) in a pupa a few days old shows very 
well the character and effects of the phagocytosis. 
Thus in the fly Blepharocera, with its eighteen days of 
prepupal and pupal condition, phagocytosis is conspicuously 
present; in the fly Holorusia, with its twelve days of pupal 
condition, histolysis is unaccompanied by phagocytosis. The 
fly in which the histolytic phenomena occupy the longer time 
is the one in which the histolysis is accompanied by phagocy- 
tosis. This is a condition not at all in consonance with Kara- 
waiew's conclusions, as quoted at the beginning of this paper. 
What is the reason for the presence of phagocytes in the 
histolysis of Blepharocera and their absence in Holorusia? To 
my mind, the extent of the metamorphic changes, the degree 
to which histolysis occurs, probably offers the explanation. 
In Blepharocera, with its highly specialized larval form, its 
peculiar and specially developed organs, the change to imago 
is radical; the histolysis of larval tissues is extensive. In 
Holorusia, with its generalized larval form, its less modified 
organs, the change to imago is accomplished with much less 
breaking down of larval organs and reformation of imaginal 
ones; the histolysis is less radical and considerable. The 
phagocytes are the agents or the assisting agents in the more 
extended and radical histolysis. 
My observations so far do not enable me to offer any evidence 
regarding the moot point touching the causal agency of the 
phagocytes in histolysis. Whether the phagocytes initiate his- 
tolysis, or merely render effective aid after the degeneration 
has been initiated independently, is a question of importance. 
