226 NATURAL HISTORY OF ARTHROPODS. 



These insects are connected with the Psyllida? by the form of the lobes of the head 

 in the young stages, a character which is preserved in the adult Membracis and its 

 near allies, as well as by the form of the abdomen, similarity of the wing-covers, and 

 saltatorial legs. 



The most aberrant members of this group belong to the sub-family Centrotida, in 

 which the prothorax is often reduced to a mere strip or triangle ; in others it is pro- 

 longed backwards into a pitchfork or trident, with the scutellum distinctly developed 

 beneath it. Some of the forms of Heteronotus have a very hymenopterous appear- 

 ance, and this is carried still farther in the form, texture, and veining of the wing- 

 covers ; others might easily be mistaken from their resemblance to the spinous ants 

 which inhabit the same localities, in Brazil and Mexico. 



More than eight hundred species have been described from Africa, temperate and 

 tropical South America, Central America, Mexico, the West Indies, and the United 

 States. Europe is singularly destitute of these insects, of which only two or three forms 

 cross her borders from the near provinces of Africa, while Brazil and the other torrid 

 countries of South America claim more than half the species of the world. Australia 

 and the East Indies possess a few species, but they form no conspicuous portion of the 

 Fauna, and belong chiefly to the Centrotida. 



Most of the insects which we have thus far noticed are mute, but we now reach 

 the CICADID^:, a group of generally large forms, which have been celebrated in classic 

 and other lands for their wondrous song. They may be recognized by their heavy 

 subconical bodies, wide, blunt head, with prominent eyes on the outer angles, ridged 

 epistoma crossed by coarse oblique ribs, bristle-shaped antennas, placed in a socket 

 beneath a ledge of the vertex, and three bead-like ocelli arranged in a triangle on the 

 middle of the cranium. The mesothorax is the largest segment, and the metathorax is 

 reduced to a narrow scale. A very conspicuous feature in all of them is a cross-like 

 prominence on the bind end of the former, which adds great firmness to this important 

 part of the chest. The wing-covers are nearly elliptical, longer than the body, parch- 

 ment-like, but generally transparent, and with a series of eight areoles at the tip ; but 

 the hind-wings are moi-e membranous, scarcely exceeding half the length of the former, 

 and with an apical series of six areoles. Their legs are short and stout, not fitted for 

 leaping, the fore-thighs quite thick, armed with two or more thick teeth, also the hind- 

 shanks are bristly, and have a series of sharp spines on each side. 



But the most distinctive peculi- 

 arity, which has no parallel in any 

 of the other groups, appears in the 

 organs of sound. These consist of 

 two large parchment sacs, ribbed 

 and gathered into numerous plaits, 

 furnished with powerful muscles, 

 and situated in large cavities at the 

 base of the abdomen. When in 

 action the air is driven with great 

 FIG. 303. cicada Hbicen, lyerman, harvest-fly. force ngainst the ribbed surfaces, and 



vibrations are set up which produce 



the sound in accordance with the number and form of the fluted spaces and ribs. Nu- 

 merous modifications prevail in the form, size, thickness, power, and relative position of 

 the parts of these organs, so that there are species which give forth an almost deafenino- 



