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the group. The most important are those which, while feeding 
upon plants, bring about no other modifications than those 
caused by diminution of vitality, ending in the entire destruction 
of the part attacked, or the death of the whole plant. 
As the study of the larve of these species will occupy no 
inconsiderable portion of my work on the family, the mere 
mention here of such well-known species as the Wheat Midge, 
which lives on the grain of wheat, the Foxtail-Grass Midge, 
on the seed of Alopecwrus pratensis, the Hessian Fly in the 
joints of the stem of Cereals, and the Pea Midge on field and 
garden peas, will suffice.* 
Other species undoubtedly feed on fungi and on rotting 
wood, being found under loose bark. Osten-Sacken records a 
species found by him on the leaves of the hickory apparently 
feeding exposed. Some are said to be inquilines, or guests in 
the galls of their congeners, while others again are believed to 
be associated with Aphides in some connection not hitherto 
understood. This however wants confirmation. 
The larval stage, we have seen, is the one to which the 
greatest interest attaches, and the progress of the gall and sim- 
ultaneous growth of the larve, offer a hitherto comparatively 
unexplored field of observation and research. A voluminous 
literature, chiefly foreign, deals with the aspect of the galls, and 
the descriptions of the known species of adult and larval 
Cecidomyide ; but little work has been done on the question of 
the actual and continuous changes in the gradually modifying 
tissues of an affected plant, due to the pressure and behaviour 
of the embedded larva. To this point my own observations 
have been mainly directed, and by means of continuous sections 
through galls of various ages, something of the life-history of 
the gall has I think been revealed. 
* Recent attention has been specially directed to the Hessian Fly from 
its appearance in England as a farm-pest on wheat and barley; and the 
economic aspects of the question have been fully discussed by Miss Ormerod 
in a small brochure, entitled ‘The Hessian Fly"; in some valuable letters 
from Prof. Riley, U.S.A., to the Times; and in Government Reports by 
Mr C. Whitehead. 
