1 88 



Tin-: APPLE LEAF HOPPER 



type has tb.rce varieties ; if it is enlarged at the hase it is not distin- 

 guished by any particular name, if it is enlarged in the middle it is 

 called vasiform. if it is enlarged at the end it is called clavate. In the 

 gall-makers the cornicles, when present, are reduced to mere pores 

 level with the surface of the body. This is probably a specialized and 

 not a primitive condition. In P. popiili-tniiisz-'crsus the cornicle is 

 present in the larva luit not in the adult. 



7^. f- 



Fig, It", niust rating types of cornicles, a, Tiiberculate type of Tjachnus longls- 

 tignia. b. Truncate type of Olialtophorus sali.x. c, Cylindrical type of Aphis, d, 

 Incrassate type of the higlier geiiei-a. 1, vasiform; 2, clavate; 3, cornicle incrassate 

 at base. 



When looking" down upon the cornicle the lai'ge circular opening 

 shows plainly. This opening is closed by a semi-circular valve, which 

 can be pulled inward b}- a long slender valvular muscle attached to its 

 inner side, and inserted on the posterior edge of the sixth abdominal 

 sternite. There is a muscle attached to the base of the cornicle and 

 inserted on the pleurite of the fifth abdominal segment, which elevates 

 the cornicle. The ornamentatit^i of the cornicle in the higher genera 

 is interesting, and may be used to a certain extent as a specific char- 

 acter. Some show only the ordinary imbrications of the cuticle of the 

 rest of the bodv. While others show onlv fine imbrications near the 



