4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



ing apparatus, the principal specialization of the larva pertains to the 

 respiratory system. The only functional respiratory apertures are a 

 pair of dorsal spiracles near the end of the abdomen, the lateral 

 spiracles being closed except at ecdysis when the tracheal linings are 

 partly pulled out through them. 



THE HEAD 



The head of a mosquito larva projects forward from the thorax in 

 line with the axis of the body, bringing the mouth parts to an anterior 

 position. In most adult insects the head hangs downward on the 

 thorax, so that the face is anterior and the mouth parts ventral. In 

 the prognathous mosquito larva the face becomes dorsal and the mouth 

 parts anterior. In going from adult to larva, therefore, instead of 

 reversing the meaning of "dorsal" and "ventral," it will be better to 

 speak of the upper and lower surfaces of the larval head, though 

 "anterior" and "posterior" in either larva or adult will be directions 

 relative to the axis of the body. 



The typical shape of the mosquito larval head is oval or ovate, 

 whether seen from above (fig. I A,B,C) or from the side (E), but 

 the upper surface is more rounded than the lower. In some species, 

 however, the head is almost rectangular in form (D). Anteriorly 

 the head bears laterally a pair of large mustachelike brushes, and 

 usually between them a small median brush, the three being supported 

 by the labrum. Shortly behind the lateral brushes arise the slender, 

 tapering, unsegmented antennae (E, Ant). Posteriorly on each side 

 of the head is a large dark spot (E) varying in size with the age of 

 the larva. These spots are the pigmented compound eyes of the adult 

 developing in the epidermis beneath the larval cuticle. Behind or 

 below each compound eye is a small, simple, presumably functional 

 larval eye (O). The lateral area of the head between the antenna and 

 the eye is the gena (Ge), that behind and below the eye the postgena 

 (Pge). Posteriorly the head abruptly narrows to the occipital fora- 

 men, which is rimmed by a darkly sclerotized band, the postocciput, 

 set off by a postoccipital sulcus. The membranous neck is usually 

 cylindrical (fig. 1 A), but in Anopheles (fig. 3 C) it is narrowed where 

 it joins the thorax, evidently to facilitate the turning of the head upside 

 down while feeding. 



The upper surface of the head (fig. 1) is differentiated into a large, 

 shieldlike central area, narrow lateral areas bearing the antennae and 

 the eyes, and a slender transverse anterior sclerite at the bases of the 

 brushes. This sclerite (A,B, Lm) is the dorsal wall of the labrum, 



