DIPTERA. 



57 



up their abode and feed upon its tissues. This does not immediately, nor in a direct 

 manner, cause the death of the plant, but, weakening its stem, renders it liable to 

 be beaten down by wind or rain, and causes it to bear inferior corn if it reach 

 maturity, Towards the end of July the larvae are full grown, and pass into 

 the pupal stage ; while at the end of August or the beginning of September the 

 adults again appear and lay their eggs on winter wheat, the larvae that are hatched 

 from these passing the winter in the pupal state and completing their development 

 in the spring, Nearly allied is the wheat-midge (G. tritici), which, as its name 

 indicates, also attacks the wheat-plant, to which it at times does great damage. 

 The female lays her eggs often in numbers not on the leaves or stems, but in 

 the heart of the blossom, and their presence either entirely prevents the formation 

 of any seed, or renders that produced of a poor kind. 



There are many other species of gall-midges which attack different kinds of 

 plants, such as the willow, hawthorn, etc., but lack of space forbids further refer- 



DEVELOPMENT OF HESSIAN FLY. 



a, Female enlarged and of natural size ; b, Abdomen of male ; c, Pupa ; d, Skin of larva forming pupa-case ; e, Larva 

 seen in profile (the line representing its nat. size) ; /, Larva from above (enlarged) ; g, Wheat-stalks infested with 

 larvte. 



ence to them. One only (Miastor metroloas) demands attention on account of the 

 remarkable powers of reproduction of its larvae. In the majority of cases insects 

 are only able to reproduce their kind after attaining the adult state, the larvae 

 being merely the young modified for a free and active existence ; but the larvae 

 of this midge, which are found under the bark of trees, possess the remarkable 

 power of producing within their bodies living young. These grow to a certain size 

 at the expense of their parent, whose vitals they devour, then rupture the empty 

 skin and start life on their own account. The second larvae repeat the same 

 process of reproduction, and so the phenomenon continues through the cold months 

 of the year. At the beginning of the summer the process comes to an end, and 

 the larvae fulfil their destiny and give rise to mature insects in the ordinary 

 manner. 



