II 



FLIES WITH AQUATIC 



207 



even the first pair of legs. The fore part of the body 

 is covered with short reddish spines, which vary in 

 shape according to the species 

 examined. In some larvae they 

 are single-pointed, in others 

 three- or four-pointed, while in 

 a third kind they divide into 

 from sixteen to twenty points. 



" The larva possesses a re- 

 markable sucking and filtering 

 apparatus in its muscular 

 pharynx. This is situated in the FlG . 7S ._ Sen?orypapilteoflarva 

 second and third segments, and aL En ga a ngiiI ith The " erves 



inner 



forms an oval body, held in its P*pi"a is two-jointed, 

 place by a number of muscles, and stiffened by a 

 complicated chitinous skeleton. Two thin and broad 

 chitinous bands extend along the hinder part of the 

 pharynx ; these become narrower and more solid in 

 front, where they give off processes for muscular 

 attachment and for the support of the mouth-organs. 

 Here the chitinous bars unite, and form a strong 

 arch, completed below by a stirrup-shaped piece. 



" When the pharynx is opened, it is found to enclose 

 t\vo chambers, an upper and a lower, which are separ- 

 ated by a horizontal floor of unusual construction. 

 The upper chamber is lined by a loose membrane, 

 which dissolves in potash solution. This can be 

 dilated by special muscles. From the hinder end of 

 this chamber proceeds the cesophagus, the entrance 

 to which is controlled by a muscular valve. The 

 lower chamber also has a loose lining, which is chitin- 

 ous, and supported by the chitinous skeleton already 



