DIPTERA OF MINNESOTA. 



27 



ing. Some flies which pierce or stab before they suck, have firm, 

 strong mouth parts for that purpose, (see Fig. 5), but the majority, 

 since they take food for the most part in a Hquid state, have mouth 

 parts adapted for that habit. 



The middle portion of the fly, the thorax, as shown in Fig. 4, 

 bears the wings and legs. Each part of the thorax seen in the 

 figure has a name, but it is unnecessary to place these technical 

 names before the reader here. Each of the six legs (only the three 

 of the right side are shown in the figure) is composed of five parts; 

 the coxa, attaching the leg to the thorax, the trochanter or second 

 joint, next the femur (generally the longest, 

 stoutest joint), next the tibia, and finally 

 the tarsus, generally composed of five small 

 joints. On the fifth or last joint are two 

 clazvs, and between them often is a pad or 

 bristle, known as the eiiipodimn. On the last 

 joint of the tarsus, below the claws, are two 

 fleshy pads (not always present) called pid- 

 z'illi (see Fig. 10). 



The halteres or balancers are short club- 

 like organs shown in Fig. 4, one of which is 

 shown on the upper and rear portion of the 

 thorax, just under the alulae or alulets. 

 These latter are two membranous scales, 

 one overlapping the other, on each side of 

 the fly, just back of the base or root of the 

 wing, well shown in our illustration. Differ- 

 ent workers ascribe . different functions 

 to the halteres, which represent the sec- 

 ond pair of wings. They may be used as 

 balancing organs, or have also auditory 

 functions. 



The wings are, in the classification 

 of the Diptera, the most important fea- 

 ture, since the different families are 

 characterized by the different arrange- 

 ment of the veins which, as seen in the 

 illustration of the House Fly, are 

 horny thickenings in the otherwise ^'^•^- ,^^^^''"1 median section 



° v-ivv.ov. through simple eye, or ocellus, 



homogenous structure of the wine- T.W,'^'^ ''"'^''K*^'^- From Lowne's 



rp, . »■ IJlowhIy. c=corneal lense; 



1 he vems are reallv double tubes an h=:so-caiied hypodermai cells 



"' of the integument; n=nerve. 



Fig. 7. Vertical section 

 through compound eye, 

 much enlarged. From 

 Lowne's "Blow Fly." 



