AQUATIC MIDGES AND SOME RELATED INSECTS. 43 



base of a poplar tree. He also found Ceratopogon lucorum Mirgen in a heap of decom- 

 posing elm leaves and succeeded in rearing them indoors in this same material Laboul- 

 bene (1869) found the larva? of an unidentified species of Ceratopogon in the ulcers or 

 injured places in elm trees where they were living in what Dufour (1845) calls "la 

 marmelade de l'Orme." These larvae were reared and the species named Ceratopogon 

 dujouri in honor of Leon Dufour by Laboulbene. Long (1902) found Ceratopogon 

 brumalis Long in great numbers on the underside of nearly dry cow dung. He also 

 found several hundred larvae of all ages on the undersurface of a piece of moist rotting 

 elm wood. He found similar larvae and pupae in the nests of the common foraging ants 

 (Eciton coecum). The larvae of Ceratopogon specularis Coquillett were found by Long 

 to live gregariously in cow dung. Larvae of Ceratopogon stenomaiis Long were found 

 by Dr. W. M. Wheeler in an ant nest, where they were moving about in the refuse 

 heaped up by the ants in certain portions of their nests. 



The larvae of Ceratopogon taxanus Long (Long, 1902) were found beneath the 

 bark of old dead trees in moist places or on the underside of very damp rotting wood. 

 The only other habitat so far as known where the larvae are commonly found is a 

 strictly aquatic one. This latter environment according to Johannsen (1905) is 

 occupied by the species having smooth wings. An examination of Malloch's (1915) 

 keys, which cover only the Illinois species of this subfamily, shows 4 genera and 22 

 species with hairy wings to 9 genera and 72 species with smooth wings. It would 

 appear, therefore (granting the supposition that smooth wings and aquatic habitat 

 for the larvae are correlated characters), that the greater number of the species are 

 aquatic, but so few species are known in the immature stages that it is impossible to 

 say whether the greater number undergoes development in water or in some more 

 distinctly terrestrial environment. 



BODY STRUCTURES. 



The bodies of the aquatic larvae are long and tapering, and their heads are propor- 

 tionally longer and slimmer than those of the semiaquatic and terrestrial forms. The 

 aquatic larvae are entirely devoid of walking appendages, and the only external body 

 structures that link them up with their near allies are the caudal filaments. These 

 have either been considered homologous with claws of the posterior prolegs or left with- 

 out any attempt at a comparison. In a permanent preparation of the larva of a Culi- 

 coidies sp. ? the author has discovered that these filaments are arranged in two groups 

 (figs. 45 and 48), which clearly suggest that they are homologous with the caudal 

 filaments of the Chironominae. Several authors have suggested that these structures, 

 since they can be made to point either forward or backward, function as locomotor 

 appendages. This observation is apparently correct. The great relative size and 

 length of these caudal filaments seem to be functional modifications, for they are sense 

 organs in other genera of the family. 



The semiaquatic species (fig. 49) found in the sap flows of injured elms here at 

 Ithaca, N. Y., resembles the one described by Laboulbene (1869), which he named 

 Ceratopogon dufouri. These larvae differ from the aquatic forms in having only poorly 

 developed caudal setae and in the presence of very short and contractile posterior pro- 

 legs, which are fused together and provided with a circle of hooked claws (fig. 50) . This 



