THE BLUEBOTTLE FLY. 83 



segment. Remembering that the top of the thorax con- 

 tains the wing muscles, can you see any reason for the 

 specialization of the mesothorax, and for the suppression 

 of the other segments ? 



Observe the shape, size, position, and texture of the 

 single pair of developed wings. Observe that these are 

 produced backwards at their bases in two short mem- 

 branes (the alulets). Draw. 



On the sides, half concealed by the alulets, find a 

 pair of knobbed, threadlike appendages (the halteres, or 

 balancers). Observe that these spring from the narrow 

 inetathorax. They represent the second pair of wings. 

 Remove, examine with low power, and draw. 



Observe the size and position of the legs. For what 

 kind of locomotion are they adapted ? Examine one with 

 a lens, to find the usual parts. How many segments in 

 the tarsus ? Observe the two claws at the end of the ter- 

 minal segment, and the pulvilli (or sucking disks) beneath 

 it. It is by means of these pulvilli that a fly walks up a 

 windowpane or across the ceiling. Count the segments 

 of the abdomen externally visible. Three terminal seg- 

 ments are withdrawn within the end of the abdomen, and 

 concealed like the small joints of a spyglass within the 

 large one. Search the sides of both thorax and abdomen 

 for spiracles. 



Development. The development of this insect can be 

 watched with less time and trouble than that of almost 

 any other; and, although its early environment is far from 

 being attractive, it teaches an important lesson in the 

 economy of nature. We cannot know the important place 

 this fly fills without knowing something of its larval life. 

 This is true of all insects. 



The eggs of the bluebottle fly are laid on flesh, 

 ordinarily on the carcasses of animals that have fallen 



