80 THE EEPORT OF THE No. 36 



The medullary, stem or branch galls differ from the preceding in that the 

 larvas confine their operations to the interior of the affected tissues, frequently 

 restricting themselves to the pith and producing rather characteristic deformities. 



Root Galls. — There are only a few root galls known, probably because of the 

 great difficulty in finding them. There appears to be no marked difference between 

 these and stem galls, aside from the point of location. 



Kccalling the fact that gall midge larvse are small, without defensive armor 

 or apparatus, with masticatory or boring organs poorly developed or absent, it is 

 obvious that this gall-making habit is one of the most important adaptations of 

 the family. The gall midges have been able to maintain themselves in hosts and 

 ill many and varied forms by adaptations which have led to their seeking susten- 

 ance and shelter in places comparatively free from invasion by other insects. Not 

 only have these small insects learned to prey upon numerous plants, but some 

 have found it advantageous to wring sustenance from their associates. The species 

 of Lestodiplosis, in particular, may be reared from a great variety of galls, and 

 the larvge have even been observed preying upon gall midge maggots, especially 

 those of Miastor. Members of this family have also learned the value of other 

 insects as food, and we now have records of a number of species preying upon 

 scale insects, various plant lice and red spider. 



Intimate relations exist between certain genera of gall midges and families 

 and species of -plants. It is perhaps sufficient to note in this connection that the 

 genus Cincticornia is practically confined to Quercus, Caryomyia to Carya, Rho- 

 palomyia largely to solidago and aster, and Ehabdophaga mostly to Salix. The 

 mere statement of these facts indicates a correlation which has been discussed more 

 fully by the speaker elsewhere and need not be dealt upon at the present time. 



5. Structural Adaptations. — It might be thought that this host of gall 

 midges with its general similarity of habit would exhibit comparatively slight 

 variations in structure. Modifications in anatomy almost invariably mean varia- 

 tions in habits, and consequently they are worthy of note, even though they be 

 but signs of unknown facts, in the same way that irregularities in the movement 

 of a celestial body may mean the existence of an unknown planet. We wish for a 

 few minutes to call attention to some of the more striking structural modifica- 

 tions. 



Antennw. — The antennae in this family present a most extraordinary range in 

 development, varying from comparatively insignificant and presumably relatively 

 useless organs with but eight segments in Tritozyga and Microcerata to the rather 

 highly specialized organs with as many as 33 segments in Lasiopfera qnerciperda. 

 There is an equally great variation in thf form of the antennal segments and their 

 sensory organs. The cylindric antennal segment is undoubtedly the more general- 

 ized type, and is the one found most frequently in the Mycetophilidne. 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 Campylomyzarias, or globose as in Joannisia, while in the Itonididinarige 

 we have a dumb-bell-shaped structure, the basal and 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. 



