28 WILLIAM T. M. FORBES 



Two other structures on the thorax are occasionally of importance 

 in some species. The dorsal part of the prothorax may be extended 

 in a pair of mushroom-shaped bodies, the patagia, or, taken together, 

 the collar. Sometimes they are called tegulas (fig. 16, sctj. They are 

 only conspicuous in the Noctuoidea, and even there are so buried in 

 vestiture as to appear merely part of the general body surface. The 

 true tegulcR (sometimes called patagia) are attached at the base of 

 the fore wing and loop about it, covering the base of the costa and the 

 whole articulation (fig. 16, tg.). The part of the mesothorax exposed 

 between the tegulae is the disc. The metathorax is narrow above, 

 widening a little to support the wings, and bears the basal hair. The 

 general surface of the thorax is divided into a considerable number 

 of sclerites, as in other insects ; but as they are^ little used in classi- 

 fication, the figure is sufficiently explanatory. 



To study the surface it must be denuded of scales and hairs. The 

 back of the insect, above the level of the wings, is the dorsum or tergum, 

 and its sclerites are tergites (set, scl) ; the sides from wings to legs, 

 are pleura, composed of pleurites (eps, epm, etc.), and the lower side, 

 between the legs, is the venter, made up of sternites (s). 



The abdomen is normally composed of ten segments, several of which 

 are usually concealed, and it bears at its end the sexual organs, the 

 most conspicuous of which, in the male, are the valves, a pair of claspers 

 for holding the female; and, in the female, the ovipositor, or instru- 

 ment for placing the eggs. 



The abdomen may be divided like the thorax into dorsum, pleura, 

 and venter, though in the absence of legs and wings the boundaries 

 may seem a bit arbitrary. The membrane on the sides is considered 

 to represent the pleura. On the first segment there is however a deep 

 groove, the tergo-pleural groove (fig. 16, tpl.), and a small pleurite 

 below it. Scent-tufts occur on the abdomen in many males, especially 

 near the base in the Noctuidas and near the apex in the Geometridae. 

 They are usually retractile in pockets when not in use, and are rarely 

 seen expanded. Those near the tip of the abdomen (on the seventh 

 segment) are called coremata. 



In the males of most species there are eight visible segments. The 

 body of the ninth (fig. 20) is reduced to a ring, the tergite of which 

 is the tegumen, and its sternite the saccus or vinculum. Attached to 

 the junction of tegumen and saccus is the valve (harpe), the name of 

 which indicates a common form. The valve may be composed of a 

 thickened dorsal edge, or costa, a central part, the valvula, or valve 

 proper, and a lower part which is strongly curved and spoon-like, the 

 sacculus. Lying in the middle line between the valves is the penis, or 



