28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



of long, spreading hairs are usually present on the end of the tenth 

 segment, and perhaps serve as a rudder during swimming. Though 

 mosquito larvae are commonly known as "wrigglers" or "wigglers" 

 they swim by lashing movements of the abdomen, which drive them 

 forward, backward, or sideways. The active larvae of Culex zigzag 

 through the water like tumbling acrobats. Anopheles, however, is a 

 true wriggler ; it swims either on the surface or under the water by 

 quick lateral movements of the abdomen and propels itself backward. 



The dorsal spiracles of the abdomen are the only breathing aper- 

 tures of the mosquito larva. The lateral spiracles are closed except 

 at the ecdyses, when they are temporarily opened to allow the tracheal 

 linings to be pulled out. Since the dorsal spiracles open into the dorsal 

 trunks of the tracheal system and the lateral spiracles into the lateral 

 trunks (fig. 10A), the dorsal spiracles cannot be supposed to be a 

 pair of lateral spiracles that have moved up onto the back. It may be 

 conceded that spiracles can change their position, but they cannot 

 change their tracheal connections. 



The spiracles of anopheline larvae lie in the floor of a shallow, 

 basinlike peritremal structure elevated on the back, the margins of 

 which are variously produced into lobes (fig. 10B). In Anopheles 

 maculipcnnis (D) there are two large, thin posterior lobes, a pair of 

 small tapering lateral lobes, and a single anterior lobe supported on 

 a transverse basal bar. The spiracles (Sp) lie anteriorly; behind 

 them is a median V-shaped sclerotization on the floor of the basin, 

 and on each posterior lobe is a weak submarginal sclerotization. As 

 the Anopheles larva feeds stretched out against the surface film of 

 the water the peritremal basin projects just above the water with the 

 spiracles freely exposed to the air. When the larva submerges, the 

 whole apparatus folds up and the lobes clamp tight together (C). 

 Imms (1908) describes three sets of paired muscles that effect the 

 closing of the lobes, which retain a bubble of air between them. When 

 the muscles relax the lobes open. Curving around the end of the 

 ninth segment beneath the ends of the posterior lobes is a narrow semi- 

 circular bar that supports on each side a small plate bearing a comb 

 of strong recurved bristles (D), or in some species is armed with 

 spines or teeth. 



In the larvae of Culicinae and Toxorhynchitinae the spiracles are 

 carried out on the end of a tube, or siphon, varying in length and 

 thickness in different genera (fig. ioE,F). The spiracles are at the 

 end of the tube and are surrounded by lobes similar to those in 

 Anopheles, but necessarily much smaller (H). When the larva is at 



