12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



labium, composed of a united pair of second maxillae. The mandibles, 

 maxillae, and labium, furthermore, have been fashioned from three 

 pairs of legs, since the original arthropods had no other organs for 

 feeding than their legs. The insect mouth parts, therefore, are all 

 outside the mouth ; the space between them may be termed the preoral 

 food cavity, but by a long-perpetuated error it has commonly been 

 called the "pharynx." For want of a revised nomenclature we still 

 speak of the upper wall of the preoral cavity as the epipharyngeal 

 surface, and call the tonguelike lobe that projects below the mouth the 

 hypopharynx. This is just a part of our heritage from the early insect 

 anatomists, who had only vertebrate names to draw from, and applied 

 them to insects on a functional rather than a morphological basis. 

 The true pharynx is a part of the stomodaeal section of the alimentary 

 canal behind the mouth. 



The labrum. — The labrum of the mosquito larva includes the small 

 transverse sclerite on the dorsal wall of the head before the clypeus 

 (fig. 1 A, Lm), and a larger membranous undersurface that bears 

 laterally the two vibratory feeding brushes (fig. 4B), and usually 

 a small median brush. The median brush is the "palatum" of mosquito 

 students, another example of misuse of a borrowed vertebrate name, 

 which in this case properly refers to the roof of the mouth cavity. 



The lateral brushes of the labrum are the organs by which those 

 larvae that feed on particles create currents in the water directed 

 toward the head, and drive a stream of water back to the mouth along 

 the epipharyngeal surface. The individual hairs of the brushes are 

 finely pectinate and serve also as combs for retaining particles filtered 

 from the water. 



The vibratory movement of the brushes is produced by a pair of 

 strongly musculated sclerites on the under side of the labrum. Simi- 

 lar sclerites are present in the larvae of Chironomidae (fig. 4 G, Tor), 

 which have no brushes, but the posterior ends of the sclerite are 

 produced into strong pointed processes (Mes) projecting freely from 

 the epipharyngeal surface. These toothed sclerites were therefore 

 called by most earlier writers "premandibles." Chaudonneret (1951), 

 however, has shown that this term is entirely inappropriate. Cook 

 (1944b) named the sclerites "messores" (harvesters) and carried 

 the term over to the mosquito larvae, in which he has been followed 

 by several recent writers, though the culicid sclerites are unarmed. 



It must be noted that the insect labrum is commonly equipped with 

 four muscles, one pair dorsal, the other ventral, all of which arise on 

 the frons. The ventral muscles are usually attached on a pair of 



