THE ABDOMEN OP A BEETLE. 19 



pair being usually more firmly united. On raising the elytra the 

 number of dorsal segments visible is almost always greater than 

 those below, and in most eases their texture is less dense and often 

 membranous. 



The breathing pores or spiracles, opening into the trachea or air 

 tubes, are located in the connecting membrane or in the upper in- 

 flexed portion of the ventral segments; an additional spiracle is 

 also usually located on the under side of the prothorax behind the 

 outer limit of the eoxal cavity. 



The anal opening is located between the last dorsal and the last 

 ventral and .just below it is the genital opening. Each side of this 

 are homy valves, sometimes of very complex structure, termed the 

 gcni/al armature. 



Where the dorsal segments are not covered by the elytra, the 

 last one is called the pijgid/ium and the next to last the propijfjidiKin. 

 The ventral segments may be either entirely free, so that the abdo- 

 men is flexible, as in the Staphylinidu', or they may be more or less 

 closely united so that the last one alone is movable. The cross su- 

 tures connecting them are usually plainly visible. Both they and 

 the dorsal segments are, however, often punctured or otherwise 

 sculptured, and pubescent, as is also the under surface in front of 

 the abdomen. 



Stridulatiitg organs, used for producing sound or sexual calls, 

 are present in a number of species, but are much less common and 

 more simple than in the Orthoptera. They usually consist of fine 

 wrinkles or ridges placed side by side, and the sound is produced ))y 

 rubbing over these some other nearby portion of the body. For the 

 most part these ridges are located upon some one of the abdominal 

 segments and are rubbed by either the elytra or the hind legs. 



The above constitute the more important external parts of a 

 beetle, the characters of which are used in determining its name and 

 position among the members of the order Coleoptera. As already 

 seen, these different parts vary much in size and form, but the 

 names above given to them apply as well to the members of one 

 family as to those of another. Many other descriptive terms will 

 also be found in the pages which follow, but they, for the most part, 

 will be self-explanatory, or wi\\ be defined in the accompanying 

 glossary. By referring to such figures as are given and by observ- 

 ing very carefully the parts of the specimen in hand, the beginner 

 need have but little hesitation in deciding as to whether the descrip- 

 tion agrees with that specimen. 



