82 INSECTS. 



5. The terminal segment, which is expanded into a long, 

 feathery tip. Draw. 



Mouth Parts. The study of the mouth parts is not so 

 easy. The parts, being soft, are difficult of separation. 

 That they are all combined into a sort of proboscis has 

 been seen already. The sheath of this proboscis consists 

 of labium and labial palpi, grown together, and split down 

 the median line of the second joint of the proboscis in 

 front. At its tip are the two flaps already noticed. The 

 structure of this tip may be studied as follows: Kill a fly 

 in the cyanide bottle, and at once cut off its head. Place 

 the head flat on a slide, face upward, and apply pressure 

 to the center of the head with the point of a pencil. This 

 will cause the proboscis to expand fully. When so ex- 

 panded, apply a drop of turpentine and a cover glass to its 

 tip, and fasten the cover glass down with a clip before 

 removing pressure. The inner surfaces of the two flaps 

 will be fully exposed, and may be studied at leisure. 

 Observe the nearly parallel ridges on these surfaces. 

 Observe that they run transversely. Consider, then, that 

 the proboscis is moved backward and forward in feeding, 

 and you will see that the structure of these parts explains 

 their action, and that the rasping, back-and-forward motion 

 utilizes the rasping surfaces formed by these transverse 

 ridges. Draw. 



Within the sheath of the proboscis there are two small, 

 elongated organs, one above the other, channeled along 

 their inner faces, making a tubular passage, through which 

 food is sucked into the pharvnx. Mandibles are wanting. 

 Maxillae are represented by rudimentary, one-jointed palpi, 

 which arise from near the middle of the basal joint of the 

 proboscis. 



Thorax, Abdomen, and Appendages. Observe the shape 

 of the thorax, and the extreme specialization of its middle 



