37G THE CANADIAN ENTOMOLOGIST 



Solidago and Aster, and Rhabdophaga mostly to Salix. The mere 

 statement of these facts indicates a correlation which has been 

 discussed more fully by the writer elsewhere and need not be 

 dwelt upon at the present tine. 



Structural adaptations. It might be thought that this host 

 of gall midges, with its general similarity of habit, would exhibit 

 com.paratively slight variations in structure. Modifications in 

 anatomy almost invariably mean variations in habits ,and conse- 

 quently they are worthy of note, even though they be but signs of 

 unknown facts, in the same way that irregularities in the move- 

 ment of a celestial body may m^an the existence of an unknown 

 planet. We wish for a few minutes to call attention to some of the 

 move structural modifications. 



AntenncB: — The antennae in this family present a most extra- 

 ordinary range in development, varying from comparatively in- 

 significant and presumably relatively useless organs with but 8 

 segments in Tritozyga and Microcerata to the rather highly 

 specialized organs with as many as 33 segments in Lasioptera 

 querciperda. There is an equally great variation in the form of 

 the antennal segment and their sensory organs. The cylindric 

 antennal segment is undoubtedly the more generalized type, as it 

 is the one found most. frequently in the Mycetophilidae. This may 

 be modified to form a cylindrical larger base and a greatly produced 

 distal stem, in some instances the latter attaining a length three 

 times that of the basal enlargement. The basal portion of the 

 antennal segment may be conical as in many Campylomyzariae or 

 globose as in Joannisia, while in the Itondidinaria? we have a dumb- 

 bell-shaped structure, the basal distal enlargements being separated 

 by a stem, with a similar constriction at the apex of the segment. 

 This peculiar modification undoubtedly means greater efficiency in 

 the sensory organs, since they are more widely separated, and is 

 characteristic of the males in one large tribe. 



The antennae of the more primitive groups, such as the Campy- 

 lomyzariae and the Heteropezin«, bear a number of peculiar sensory 

 organs, the more remarkable of which are the so-called stemmed 

 disks in the genus Monardia. These are probably olfactory in 

 function. 



The Itonididinae, as limited by us, may be easily recognized 



