GLASGOW SOCIETY OF FIELD NATURALISTS. 155 



Taking a general survey of the animal kingdom, we find gall- 

 makers are confined to the sub-kingdom Arthropoda, and, with the 

 exception of cei-tain mites {Acaridce), belonging to the class Ai'ach- 

 nida (spiders), to the Insecta. Most of the orders of insects pos- 

 sess gall-makers, but it is in the Hymenoptera and Diptera that 

 we get the gall-makers par 'excellence. In the rest, gall-making 

 exists only as an accidental feature found solitarily here and 

 there throughout the orders ; the Homoptera (which includes the 

 Plant-lice) showing perhaps, like the Acaridce, a tendency to 

 aggregation. 



Each of the two orders just cited possesses a group or family in 

 which gall-making forms a prominent and characteristic feature, 

 and is the mode of life of the majority of its component species. 

 These two families are the Cynipidse among the Hymeuoptera, 

 and the Cecidomyidse among the Diptera. For an account of the 

 former I cannot do better than refer you to the paper on the 

 Scottish species by Mr. P. Cameron, junr., published in the second 

 part of our " Transactions " (Session 1873-74). The Cecidomyidse 

 I propose to consider in this paper. 



It may be well to preface my observations with a few very brief 

 remarks on the position of our group. 



The Diptera are known at once from all other insects by having 

 two wings instead of four, the posterior pair being represented by 

 peculiar clubbed appendages termed halteres or balancers. 



The larvae of Diptera may be broadly arranged into two groups 

 by the mode of pupating. In the one the larva changes to a pupa 

 inside the larval skin, which hardens and becomes a compact and 

 more or less sculptured case, protecting the pupa which lies free 

 inside ; this case receives the name puparium. In the other group 

 the larval skin is cast ofl", and does not become a puparium, the 

 pupa being completely swathed in a thin horny envelope, as we 

 see in the pupa of most insects, for example that of any moth. 

 Upon the manner in which the perfect insect emerges from the 

 pupa are founded the two sub-orders into which the Diptera are 

 divided. 



The Orthorhapha split the encasing membrane in the form of a 

 longitudinal or "P -shaped dorsal fissure. The Cyclorhapha emerge 

 by pushing out the end of the puparium as a i-ound lid-like valve. 



The larvse of the sub-order Cyclorhapha do not possess a difieren- 

 tiated head, and the mouth organs are represented by a pair of 



