6 PHYLUM ARTHROPODA 



pair of wings, possessed by most insects. These are a pair of 

 minute, white, knobbed organs, which project backward from the 

 posterior wall of the somite, each one being covered by the basal 

 lobe of the wing on that side. They have a sensory fimction. 



The abdomen is composed of eight somites in the male fly and 

 nine in the female. Of these, however, four somites are much 

 larger than the others and make up the greater part of the abdo- 

 men. The sixth, seventh, and eighth in the male are very small 

 and rudimentary. In the female the posterior four form a long, 

 tubular ovipositor, which is usually telescoped into the abdomen 

 but can often be squeezed out by a little pressure. Each of the 

 five anterior abdominal somites has a pair of spiracles. Find 

 them. 



Exercise 1. Draw an outline of the dorsal aspect of the fly on a scale 

 of about lo, indicating the segmentation and the parts observed, 

 including the venation of the wings. Label all the parts observed. 



Exercise 2. Turn the fly over on its back and draw one of its legs on 

 a large scale. The names of the different segments of the leg may 

 be obtained from Exercise 3 on page 3. Note, between the two 

 claws on each foot, the two pulvilli — the hairy adhesive pads by 

 means of whose sticky secretions the fly can walk on an inverted 

 surface. 



Exercise 3, Draw on a large scale a side view of the head with the 

 proboscis extended. Note carefuUy the form of the antennae and 

 of the proboscis. The latter is homologous to the under lip, or 

 labium, of other insects. 



