The species belonging to this family, though small and easily distinguished from most other Diptera, are exceedingly abundant and subsist in the larval stage under quite varied conditions. The majority of forms live upon plants and a goodly proportion produce galls. These peculiar structures occur upon the roots, root stalks or underground buds, along the stem, on the branches, on the leaves or even among the flowers or flower heads as the case may be. One genus for example, Rhopalomyia,

more »

... all parts of various Solidagos, except perhaps the root, the galls being quite varied in character and the adults from the same representing distinct species and, so far as known to us, coming only from galls possessing certain characters. On the other hand, Asphondylia monacha O. S., a most striking form, occurs not only in terminal rosette galls on the narrow-leaved Solidago, Euthamia lanceolata and E. graminifolia, but may breed in apparently unaffected :florets of the same plant or may be found in what we have designated as adherent galls on Solidago canadensis and S. se1·otina. These latter structures are inhabited by two species belonging to as many genera and appear to be produced by the female laying eggs between the closely apposed young leaves in the rapidly growing bud. The larvre cause a depression on each surface and the margins adhere, so that when the plant develops and the leaves turn down, the pair affected adhere at the point of injury though their bases are an inch or more apart. The form of the gall appears to be determined largely by the location and number of eggs the female deposits; for example, the midrib deformity on ash leaves, known as the gall of Cecidomyia pellex, may range in length from about 1/2 to 2% inches. It appears to develop directly as a result of the larval irritation on the upper surface of the midrib; the size of the gall being proportionate to the number of larvre, small ones having perhaps five or six, while the largest may have as many as 50 to 60. Certain species breed in more or less regularly rolled leaves, and in this case there seems to be a comparatively slight irritation and the form of the roll is governed mostly by the location of the larvre and the structure of the leaf. Other species subsist in more or less irregular depressions, and here again the irritation is comparatively slight. There is one form, for example, which produces a slightly depressed rectangular area on the by guest