THE HORSEFLIES 23 



belong to the same family of insects (Muscidae), they differ 

 nevertheless greatly in their powers of disease transmission, the 

 former relating to indirect infection and the latter to direct 

 infection. 



With a specimen of each species of fly before you, note the 

 distinguishing features, indicating the same by means of separate 

 drawings of the parts, and by description in your notebooks. 



a. Mouthparts; note the characteristic position of these organs 

 at rest. 



b. Wing venation; draw the right wing of each species, care- 

 fully drawing in the wing veins. Note the differences in venation 

 by crossing (x) the parts that vary, both cells and veins. 



c. Coloration; indicate any differences in color, or color mark- 

 ings, that you may observe. 



d. Note any other differences in position of the wings, relative 

 length of body, size, etc. 



e. Sexual differences; ask your instructor for specimens of the 

 housefly representing the two sexes. Note that in the female 

 the compound eyes are widely separated, whereas in the male 

 the dorsal borders come close together. In the female the 

 terminal segments are protrusible, which should be demonstrated 

 by pinching the abdomen with the finger or forceps. The pro- 

 trusible segments make up the ovipositor. 



f. Study a life history preparation of both the housefly and 

 the stablefly, showing the egg, larva and pupa. Compare es- 

 pecially the posterior spiracles of the larva, and pupa with refer- 

 ences to position, form and size. (Draw.) 



