on the larvae of Muscidae. 27 
to the parasitic mode of life of the imago and the diminution of 
the powers of flight necessary for providing the proper environments 
for the larvae, those changes in the mode of evolution of the larvae 
were produced which distinguish the Pupipara now. 
A far distant past must have witnessed the evolution of the 
different modes of larval development of coprophagous flies; an abun- 
dance of forms must have existed at that time, and an intense struggle 
been going on among them, in order to produce the variety of larval 
development existing at present. The few palaeontological data in 
our possession tend to confirm this view; for instance, Oswald Heer’s 
Tertiary Fauna of Oeningen is remarkably rich in coprophagous 
insects. 
There are species nevertheless, among the typical coprophagous 
diptera, which are in open contradiction to the general result which 
we have reached about that group: the diminution of their fecundity. 
In this respect, the common house fly (Musca domestica) deserves 
our especial attention. It lays a comparatively large number of small 
eggs (120— 160) and its larvae pass through the normal three stages 
of growth. It remains to explain how the house fly can, under such 
eircumstances, compete with the other coprophagous flies? The ex- 
planation may perhaps be found in the very domesticity of the 
house-fly. Unable to compete with the other flies, it sought a refuge 
around human dwellings, where it had no dangerous competitors. 
Its dependence on human society is so great, that it is very seldom 
found in abundance in uninhabited distriets. (Zetterstedt mentions 
such an instance; another was observed in North- America; comp. 
Psyche, Vol. II, p. 339.) 
It would be most interesting to study the life habits of european 
flies in extra-european regions. Musca corvina for instance, as has 
been shown, has a two-fold mode of development; it would be worth 
while to inquire about its life-history in Taity or the Philippine 
Islands. — Musca domestiea, in New-Zealand, erowds out the native 
blue-bottle fly; what are its advantages in that struggle ? 
Whether Mr. Portchinski’s very ingenious generalizations are 
accepted or not, it must be acknowledged that he has discovered a 
great number of interesting biological facts, and has opened a new 
field for most important inquiries. 
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