11 



these, yet those who <irc but beginners in entomology arc frequently puzzled, 

 in reading the description of a part of the body of an insect, to know in what 

 sense the author uses these terms ; for example, whether " length " means in 

 the direction of the longest diameter of the part, or in the direction of the 

 length of the insect; but by knowing that these terms are always used with 

 reference to the whole insect, there will be no difficulty in understanding the 

 description. It often happens that by following this rule rigidly the width of 

 a part qxceeds its length, yet this must not cause us to vary from it. 



The body of the insect is naturally divided into three distinct parts, each 

 bearing certain appendages. 



First. The head (Fig. 1, hd) and its appendages, the antemice (Fig. 1, an), 

 and 2^alpi (Fig. 2, pi). 



Second. The thorax (Fig. 1, th) and its appendages, the wings and legs. 



Third. The abdomen (Fig. 1, ah) and its ajipendages, the cerci (Fig. 1, a-), 

 and ovipositor (Fig. 1, ov). 



The head varies considerably in shape, yet the typical -form may be con- 

 sidered an oblate spheroid, with the longitudinal diameter (from the neck 

 through to the face) the shortest, and its perpendicular diameter longest. In 

 some species the upper portion of the front is prolonged into a cone or pyr- 

 amid of greater or less length (as in Tryxalis, Opomala, &c-.) ; in one genus 

 (^Acrolophitus) the vertex rises obliquely upward in the form of a short cone 

 or jjyi'i^mid. Viewed from the side it presents, in many species, a triangle, 

 the face, which forms the longest line, being directed from the vertex ob- 

 liquely under toward the breast {Opomala, Oxycoryphus, Stenobothrus, &c.) ; 

 in other species it presents a parallelogram, the greatest length being up 

 and down {CEdlpoda, Acridium, Caloptenus, Pezotettix, &c.) 



In describing the head, its external surface may be considered with ref- 

 erence to four planes — the dorsum, the two sides, and the front. 



If a line be drawn across the back part from the posterior margin of one 

 eye to the posterior margin of the other, the portion lying behind this line, 

 reaching to the margin of the pronotum, will represent the occiput.* 



* I am aware that I embrace in this area the portion called the vertex by some ento- 

 mologists, the term occiput being applied by them to that part of the skull surrounding 

 the occipital foramen. But as no use of the under portion of this division of the skull 

 is made in describing genera or species, I have limited the term to the upper part, and 

 have extended the area forward to the eyes. This necessarily limits the vertex. But 

 if we take into consideration the fact that in this family the mouth is bent downward 



