286 The Scottish Naturalist. 



show that the number of hurtful species of Cecidomyidae is con- 

 siderable ; and the gall makers injurious to cultivated plants will 

 be noticed below. Let us now return to the larvae for a little. 

 The life-histories of the various species differ according to whether 

 they form (or live as guests in) galls, or feed in undistorted tissues 

 of plants, or in fungi, or in decaying substances. Many of them 

 are easily reared ; but this is by no means the case with others ; 

 and many, especially among the gall makers, as already mentioned, 

 have not yet been obtained in the perfect condition. The larvae, 

 when full-fed, generally spin thin white cocoons for their pro- 

 tection in the next or pupal state. The cocoons are very small, 

 seldom exceeding ^ inch in length. Frequently the cocoons are 

 formed in the habitats of the larvae, but often the latter creep into 

 the soil before spinning up ; and when this is their habit, they are 

 more difficult to rear. 



Before quitting this part of the subject, it should be mentioned 

 that Professor Wagner discovered, in 1861, larvae, evidently of a 

 midge of this family, living gregariously below bark. In these, 

 offspring were produced inside the bodies of the older larvae. The 

 young ones thus formed grow for a time inside the body of the 

 parent larva at the expense of the latter, which ultimately is re- 

 duced to little more than the skin. This peculiar development 

 has been amply confirmed by Leuckart and by other zoologists. Tn 

 this way the usual course of development has been curtailed very 

 greatly ; and the stages of egg, pupa, and imago, are dispensed with. 



In the usual course of development in the Cecidomyidae, as a 

 group, the pupa casts off the larval skin (instead of being enclosed 

 in it as in the diptera belonging to the Muscidae), and shows traces 

 of the future form of the insect. When the perfect insect is ready 

 to come out, it splits the pupa skin on the front half of the back, 

 making a slit, running lengthwise alone, or lengthwise, with one 

 across its front in the shape of a T; and through the slit it crawls out. 



The Cecidomydae belong to a division of Diptera, called Nema- 

 tocera, characterised by having at least six joints in the antennae; 

 which are therefore thread-like, or frequently resemble a row of small, 

 hairy beads. The Gall-midges are all of small size, usually under 

 Y2 in. in length, but the sub-genus Aspliondylia includes species 

 from -~ to i in. long. They are slender-bodied, pale, or dark brown, 

 or orange-red ; and the legs are long and slender. The wings have 

 no alulae (i.e., small, nearly free lobes at the hinder angles, as in 



