4 



piece but the true thorax consists of three rings : what appears to be the 

 whole of the thorax from above being really the upper segment of the first 

 ring. This first ring is called the pro-thorax, and attached to the lower por- 

 tion of it are the first pair of legs. The upper portion, just referred to, and 

 the portion usually meant when the thorax is spoken of, is very variable in 

 shape ; it has an anterior margin by which it is connected to the head, a 

 posterior margin connecting it to the next segment ; two side or lateral 

 margins often thickened or notched ; .two anterior angles at the junction of 

 the anterior and lateral margins ; two posterior angles at the junction of the 

 posterior and lateral margins (but these are often so rounded off that no angle 

 is visible). The portion of the thorax by which it seems attached to the 

 elytra, that is the posterior margin, is usually called the base; the front edge 

 is the apex ; and, consequently, the anterior and posterior angles are often 

 known as the apical and basal angles respectively. The upper surface of the 

 thorax is often furnished with a central channel, on each side of which is 

 the disc, while near the basal angles are frequently distinct pits, the basal 

 fovea, often thickly punctured. The second ring or segment of the thorax 

 (meso-thorax) carries below the second pair of legs, while attached to the 

 upper portion of it, and therefore nearly covering it, are the anterior wings 

 {elytra.) Just at the place where the suture of the elytra would join the 

 groove between the thorax and elytra is usually to be seen a small shield - 

 shaped surface, the scutellum, and this is the only uncovered portion of the 

 second thoracic segment. The hind segment of the thorax {meta-thorax), 

 is quite covered from view above where the true wings are attached, while the 

 hinder pair of legs are attached to its lower margin. 



The legs are always six in number, in three pairs, called respectively 

 anterior, middle, and posterior. Each leg consists of four portions, viz. — 

 a coxa or hip, usually forming a flat plate, by which it is attached to the 

 underside of the thoracic segment ; a femur or thigh, usually the thickest 

 portion, and which bears near its place of junction with the coxa a small 

 process called the trochanter ; a tibia or shank attached to the extremity of 

 the femur — the joint being called the knee ; and a tarsus or foot, consisting 

 typically of five joints, often hairy beneath, the terminal one being armed with 

 a pair of claws. Iu the males of many species some of the tarsal joints be- 

 come much widened, while in the male Dytiscus these widened joints form a 

 circular plate, the surface of which is furnished with suckers. 



The elytra, or wing-cases, next deserve mention. These may be smooth, 

 covered with irregular punctures, marked with fine lines {striae) or grooves 

 {sulci) usually running from the base (nearest the thorax) to the apex (the 

 point behind). These striae may be smooth {striate), or in the striae there 



