i86 



FIELD ZOOLOGY. 



The compound eyes of all the non-parasitic dipters 

 are many-faceted and large and placed well forward; 

 and their convexity is such as to cause them to project 

 considerably from the head, giving the flies keen and 

 comparatively accurate sight. It is very difficult to 

 catch a fly napping. In addition, some of the flies have 

 eyes with facets of two sizes; these are flies spending the 

 larval and pupal stages in the water, and are called 

 midges. 



FIG. 75. Ocelli and compound eyes of a fly, Phormia regina. A, male; B, 

 female. (Folsom.) 



The dipters reproduce by complete metamorphosis. 

 The typical larva hatched from the egg is a white grub, 

 or maggot, as it is popularly called. The eggs are laid 

 in some mass of decaying matter, some filth, either animal 

 of vegetable ; hence the maggot has no need for the effect- 

 ive biting, piercing, or sucking mouth-parts with which 

 other larvae are provided. It is simply a helpless, footless, 

 sometimes headless animal, obtaining its food osmotically 

 through the skin. The larval moultings are usually rapid, 

 and the pupal stage is soon reached. In this stage, in 

 some species of dipters, the pupa looks not unlike a brown 

 seed ; it might well be mistaken for one if it were the pupa 

 of a house fly. When the pupa case is discarded, there 



