352 
ZOOLOGY: E. P. FELT 
knowledge of the fauna in the more remote regions. Furthermore, 
the more primitive genera, such as Lestremia, Campylomyza, Porri- 
condyla, Dasyneura, Ohgotrophus, AsphondyHa, Lasioptera, Contarinia 
and Lestodiplosis, to take representatives from the various tribes, 
are found on most of the continental areas. They are represented 
among Hving forms by numerous species, many of them capable of sub- 
sisting under comparatively simple conditions and therefore not easily 
exterminated or isolated by adverse climatic changes. 
It is noteworthy that of the seven genera known from the Baltic 
Amber, six are recorded also from Australia, three from New Zealand 
and two from Africa, and in all probability more of these genera occur 
in the land areas of the Southern Hemisphere. The African, Australian, 
New Zealand and South American fsiunae appear to contain a consid- 
erable number of ancient, highly specialized offshoots from the some- 
what primitive world-wide genera (Hkewise represented) mentioned 
above and their occurrence suggests a zoological isolation where only 
the more vigorous or adaptable would estabHsh themselves and where 
the natural tendency to variation would consequently be less subject 
to interference on the part of closely related strains or species in the 
process of formation. 
One of the striking pecuHarities in distribution is the occurrence of 
the genus Aplonyx in the Northern Hemisphere, where it is known 
only from the Mediterranean region and the vicinity of Salt Lake, 
Utah — ^locaHties favored by both host plants and insects. Species of 
Didactylomyia, a very pecuhar form, occur in both North America 
and India, while the closely related Erosomyia and Indodiplosis are 
occidental and oriental, respectively. 
The above and other data which need not be discussed in detail 
here, suggest no connection between food habits and a general distri- 
bution, since there does not appear to be a better representation of 
midges, such as Lestremia and Porricondyla breeding in decaying vege- 
table or woody tissues, materials which might easily drift to distant 
shores, than there is of bud or leaf -inhabiting forms which find only 
temporary shelter in plants and transform in the soil, such as species 
of Dasyneura and Contarinia. The same is true of species passing 
most of their existence within plant tissues, such as Lasioptera and 
Rhabdophaga, forms most likely to be carried great distances with the 
host plant. An equally wide distribution is true of predaceous midges 
with only a secondary relation to plants, such as Aphidoletes, Myco- 
diplosis and Arthrocnodax. 
It is possible that some species may be widely disseminated through 
