182 DIPTERA OF NORTH AMERICA. 



in Wiegmann's Arcbiv, vol. vii. p. 233, with a plate) and what I 

 have found confirmed by my own observations, may be reduced to 

 the following: The horny parts of the head consist of a ring with 

 two processes extended backwards; a soft, fleshy swelling which 

 protrudes through this ring is taken by Ratzeburg for the labium ; 

 two openings in the upper part of the ring emit a pair of two- 

 jointed organs which this author and L. Dufour believed to be 

 palpi, but which I would rather consider as rudimental antennae, 

 especially on account of their position on the upper side of the 

 head. (Laboulbene and Ferris entertained the same view.) 



On the under side of the body, at the juncture of the first 

 thoracic segment with the supernumerary (14th) segment, there is 

 a horny, more or less elongated piece, projecting with its anterior 

 part, whereas its posterior end is concealed under the skin of the 

 first thoracic segment, and more or less translucent. This organ, 

 the use or the homology of which is unknown, is peculiar to the 

 larvae of Cecidomyia, and seems to be seldom wanting. (I found 

 under the bark of a tree a full-grown larva which, for its structure 

 I believe to be a Cecidomyia, although it showed no trace of this 

 breastbone.) It may be that this organ is used for locomotion, 

 although I hardly would consider it as homologous to the pseudo- 

 pods of the Iarva3 of Chironomus and Ceratopoyon. If the sup- 

 plementary (14th) segment be considered as a part of the head, 

 this breastbone might be taken for the mentum, in analogy to the 

 horny mentum of the larva? of the Tipularice. The form of this 

 organ is variable in different species ; sometimes it ends anteriorly 

 in two points, with an excavation between them ; sometimes in 

 one elongated point ; or it is serrated, etc. 



The remaining part of the under side of the body sometimes 

 shows other organs of locomotion. The larva of Gee. entpmophila, 

 according to Ferris, has three slender, elongated, pointed, sub- 

 corneous, approximated projections in the middle of every ventral 

 segment. Cec. fuscicollis Bouche (Bouche, ]N"aturg. der Ins. p. 

 25), has a pair of elongated, pointed pseudopods under each 

 thoracic segment, and three such pseudopods under each abdomi- 

 nal segment. Bouche's figure of the latter closely resembles 

 Perry's figure of the pseudopods of Cec. entomophila. 



The motions of the larvae, except those few, living on the surface 

 of the leaves, are generally slow; but those which change their 

 abode before assuming the pupa state become very active about 



