6 DIPTERA OF NORTH AMERICA. [PART IV. 



The body of the larvae is grub-like, of a uniform grayish, 

 brownish, or whitish color. It consists of twelve segments 

 (counting the anal segment among them). The nature of the 

 outer integuments depends on the mode of life of the larva. 

 The larvae of Ctenophora, living in wood, have a soft, white, 

 smooth skin, similar to that of the larvae of longicorn beetles or 

 of the Asilidse, living in similar conditions. The larvae of Tipula, 

 living in the soil, or the larvas of those species of Ctenophora 

 which are found in wood so far decomposed as to be like soil or 

 vegetable mould, have a much tougher skin, and are covered with 

 a microscopic, appressed pubescence. This toughness, as well 

 as some stiff bristles, scattered over the surface of the skin, is 

 probably useful in burrowing. Thus the larva of Trichocera, 

 digging in vegetable mould or in fungi, is covered, according to 

 Perris, with microscopic erect bristles ; the larva of Ula, living 

 in fungi, has, according to the same author, still longer bristles. 

 The larvse living in water (as some Limnobina) are soft and 

 slimy, of a dirty greenish color, and with a peculiar clothing of 

 appressed microscopic hairs, not unlike those of the. larvae of 

 Stratiomyia. The most anomalous of all the Tipulideous larvae 

 are those of the Cylindrotomina. That of the Cylindrotoma dis- 

 tinctissima lives upon the leaves of plants, as Anemone, Viola, 

 Stellaria, almost like a caterpillar ; it is green, with a crest along 

 the back, consisting of a row of fleshy processes. The larva of 

 Cylindrotoma (Phalaerocera) replicata, according to Degeer, 

 lives in the water, on water-plants, and is distinguished by 

 numerous filaments, which, although resembling spines, are 

 flexible and hollow on the inside. Degeer took them for organs 

 of respiration. 



The organs of locomotion of the larvae generally consist in 

 transverse swellings on the under side of the body provided with 

 exceedingly minute, stiff bristles. Sometimes these swellings run 

 round the whole body ; in such a case, their dorsal portion is less 

 developed than the ventral. The anal end of the body is truncate, 

 and the two spiracles are placed upon the truncature. The 

 margins of the latter are for the most part provided with fleshy 

 retractile processes of various size and shape, usually four, some- 

 times six* or more. The truncature can be contracted at the will 

 of the larva, and then the fleshy processes are shortened and the 

 spiracles are inclosed in the cavity thus formed at the end of the 



