The bo(h varies in form from the most elongated and thread like to 

 short or circular, from the thickest to forms so flattened that they may 

 live in the narrowest crevices They are convex above and below, or 

 flattened or concave above and convex below. 



The //t'(?'/ serves by its position to separate the two leading sid)- 

 orders but aside from this it is subject to most extreme modification. It 

 is cvlindrical. often elongate in ReduviidiE 2J\<X Nabidte, decidedly flatten- 

 ed in Cor.idie and allied families. In the Homoptem the front is verv 

 often protluced, the most extreme m(xiification of this part occuring in 

 the Fulgoridcp. 



The eyes are usually prominent organs, standing out at the sides of 

 the head: thev serve rather as land marks — by which to locate the other 

 organs of the head^than as distinctive in themselves. 



The f»tY/// are commonlv present and by their absence or by their 

 relation to the eyes serve to define some minor groups. 



The antenncF are never particularly elongated, usually compo.sed of 

 few joints and as a rule but slightly modified. They run from filiform in 

 the lower Homoptera to setiform in Ciada and allies: and are mostlv 

 filiform, with the terminal joints either slender or else slightly enlarged 

 in the Hhroptera. In a few cases the joint next the last is much flatten- 

 ed and broadened or otherwise modified. They are truly capitate onlv 

 in the Liotheidce. 



The labrum is usuallv verv small, but occasionallv with the clvpeus 

 furnishes good characters for separation of genera and species. The seta; 

 of the mouth vary greatly in length, but are of little value in determin- 

 ing the relation of groups. 



The labium is an important structural element. It forms the sheath 

 ibr the setae, and is termed the beak or rostrum. It consists of three or 

 four joints except in the Pediculidae where it is apparently devoid of arti- 

 culation. By its origin at the front of the head indicating the h(.rizontal 

 position, or at the sternal border of the head indicating the vertical posi- 

 tion, it serves to distinguish the Heteroplera and Homoptera and bv its 

 separation from or apparent union with the sternum it .serves to divide 

 the Homoplera into two minor groups. Furthermore the form of the 

 basal joint and the comparative length of the joints are points of great 

 value in determining relationships. 



The thorax in its modifications corresponds in general with the 

 habits of the groups, whether aquatic, terrestrial or aerial. 



'Y\\t prothorax is often minute and weak, again enormously deve- 

 loped and overshadowing all other parts as in Membracidae. It is trans- 

 verselv sutured in Reduviidae. 



