382 DIPTERA. 



from transverse swellings on the under side of the body. 

 "The end of the body is truncated, and the two spiracles are 

 placed upon the truncature," from the edge of which part arise 

 usually four retractile processes. 



In the aquatic larva of Ptychoptera there is a long respira- 

 tory tube at the end of the body. The pupae (Fig. 299, under 

 side, enlarged twice, represents a pupa of this family) 

 have usually on the thorax two horn-like processes, 

 representing the thoracic spiracles, and in Ptychoptera 

 one of these processes acquires a great length, in order 

 to allow the pupa to breath under water. 



The Tipulids, like other flies with soft bodies which 

 contract in drying, should, as Osteu Sacken suggests, 

 be studied from fresh specimens, especially when the 

 thorax and abdomen, with the ovipositor, are to be ex- 

 rig. 299. amined. The Tipulids of the United States, east of the 

 Mississippi river, closely represent those of Europe, while Os- 

 ten Sacken states that a few species are found to be common to 

 both countries ; and he farther states, with regard to the Tip- 

 uli dee, that "whenever the North American fauna differs from 

 the European in the occurrence of a peculiar generic form, or in 

 a marked prevalence of another, this difference is due, either to 

 an admixture of South American forms, or of forms peculiar 



to the amber fauna." 



The genus Tipula com- 

 prises the largest individuals 

 of the family, and the species 

 may be seen early in May fly- 

 ing over grassy fields. The 



larvse live in garden mould and under moss in fields and woods. 

 T. trivtttata Say is one of our most common species. 



In the genus Limnobia the body is very slender and delicate, 

 though stouter than in Dicranomyia, a closely allied genus, the 

 larvue of which are probably aquatic. "The larvae live in de- 

 caying vegetable matter, especially in wood and fungi." ' ' Van 

 Roser discovered the larvae of the European L. annulus (closely 

 allied to L. cinctipes Say) in decayed wood. They are like an 

 earth-worm in size, as well as in color, and line their burrows 

 with a kind of silken web." (Osten Sacken.) 



