Several species of HEMIPTERA-HETEROPTERA are habitual parasites of man, and others occur as occasional or accidental parasites. Of all these, the most important and widespread are the bed-bugs, belonging to the genus _Cimex_ (= _Acanthia_). THE BED-BUGS--The bed-bugs are characterized by a much flattened oval body, with the short, broad head unconstricted behind, and fitting into the strongly excavated anterior margin of the thorax. The compound eyes are prominent, simple eyes lacking. Antennæ four-jointed, the first segment short, the second long and thick, and the third and fourth slender. The tarsi are short and three segmented. It is often assumed in the literature of the subject that there is but a single species of _Cimex_ attacking man, but several such species are to be recognized. These are distinguishable by the characters given in Chapter XII. We shall consider especially _Cimex lectularius_, the most common and widespread species. _Cimex lectularius_ (= _Acanthia lectularia_, _Clinocoris lectularius_), is one of the most cosmopolitan of human parasites but, like the lice, it has been comparatively little studied until recent years, when the possibility that it may be concerned with the transmission of various diseases has awakened interest in the details of its life-history and habits. [Illustration: 70. Cimex lectularius adult and eggs. Photograph by M. V. S.] The adult insect (fig. 70) is 4-5 mm. long by 3 mm. broad, reddish brown in color, with the beak and body appendages lighter in color. The short, broad and somewhat rectangular head has no neck-like constriction but fits into the broadly semilunar prothorax. The four segmented labium or proboscis encloses the lancet-like maxillæ and mandibles. The distal of the four antennal segments is slightly club-shaped. The prothorax is characteristic of the species, being deeply incised anteriorly and with its thin lateral margins somewhat turned up. The mesothorax is triangular, with the apex posteriorly, and bears the greatly atrophied first pair of wings. There is no trace of the metathoracic pair. The greatly flattened abdomen has eight visible segments, though in reality the first is greatly reduced and has been disregarded by most writers. The body is densely covered with short bristles and hairs, the former being peculiarly saber-shaped structures sharply toothed at the apex and along the convex side (fig. 159_b_).