EXPLANATION OF TERMS USED. 51 
to discuss some of the more important species in this connection. 
Outside of the United States some of these are recognized as among 
the most serious pests, as the sugar-cane leafhopper (Perkinsiella 
saccharicida Kirk.), which has in recent years caused a loss of many 
millions of dollars to the sugar crop in Hawaii. We have also a 
species common in the Southern States which attacks corn and 
which has, at_times, been noted as very abundant and destructive. 
While it may appear unnecessary to discuss the details of classifica- 
tion or of structure in these various groups, the fact that some of the 
differences presented are such as to have a very important bearing 
on the distribution or the methods of control makes some such con- 
sideration necessary. Moreover, there is a quite important difference 
in the parasitic. enemies which may be found to occur on the different 
forms, and this alone would be ground for a careful designation be- 
tween forms which are essentially different although bearing the same 
common name. 
EXPLANATION OF TERMS USED. 
While it is possible in the description of the different insects treated 
here to use a number of common terms, such as head, wings, legs, 
abdomen, eyes, face, etc., and the descriptions are therefore intelli- 
gible to anyone so far as these go, it is necessary for the sake of pre- 
cision in some instances to use terms which are less generally known, 
or at least not definitely applied. An explanation, therefore, of a 
few terms which are really necessary for the accurate description of 
the different forms mentioned will be given in order to make the paper 
of service to those who have no technical knowledge of entomology, 
but whose acquaintance with ordinary English should enable them 
to place the particular insects which are under discussion. 
The term vertex is used for the upper surface of the head between 
the eyes and extending to the front border, which may merge gradu- 
ally into the front or the face. The frons, or front, is the part of the 
face lying between the sutures and extending down nearly to the lower 
border. At the sides of this are portions next the eyes, which are 
termed the cheek and below the front a part called clypeus, at the 
sides of which are the lore. The central part of the body which bears 
the wings and legs is termed the thorax, and the upper portion of the 
first segment is known as the pronotum. The front wings are termed 
elytra and are usually thicker and stronger than the hind pair, which 
are concealed beneath the front ones when at rest. The hinder dis- 
tinctly segmented part of the body or abdomen may be entirely hidden 
above by the wings, but in short-winged forms is more or less exposed. 
The parts of greatest importance on the abdomen for purposes of 
description are the terminal segments, including the genitalia. In 
the female the last ventral segment is frequently of a particular shape 
or structure for different species, and in many groups is of the 
greatest service for description. It is followed by the sheaths of the 
