14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



"clypeus" is the entire frontoclypeal area of the upper head wall be- 

 tween the cleavage lines. The sclerites in question, being in the 

 ventral wall of the labrum and giving attachment to the ventral labral 

 muscles, practically identify themselves as the tormae, and they have 

 been regarded as such by Anthon (1943a), Schremmer (1949, 1950), 

 and Menees (1958b). If it is desirable to keep the term "messor," 

 it might be restricted to the free prongs of the tormae where they 

 occur (fig. 4G, Mes). 



The tormae of an Anopheles larva (fig. 4 C, Tor) are elongate 

 sclerites lying mesad of the brushes. Each torma is connected by its 

 tapering anterior end with the base of the corresponding brush ; 

 posteriorly it is hinged to a small sclerite (c) in the cranial margin. 

 A connective plate (a) lies between the torma and the base of the 

 brush. A single muscle (mcl) from the frontal region is attached by a 

 long tendon to a small point anteriorly on the lateral margin of the 

 torma. Cook ( 1944a) ascribes a second posterior muscle to the torma 

 of Anopheles, but this muscle, as shown by Farnsworth ( 1947) and by 

 Schremmer (1949), belongs to a V-shaped sclerite of the epipharyn- 

 geal wall between the posterior ends of the tormae. 



In the culicine mosquitoes the tormal apparatus is somewhat more 

 complex than in Anopheles. In Aedes aegypti (fig. 4 D) the tormae 

 have the same relation to the brushes and the cranial margin as in 

 Anopheles, but each torma is specifically hinged posteriorly (e) to 

 a detached triangular plate (b) of the cranial wall, and anteriorly (d) 

 to the end of a transverse epipharyngeal bar (/) . Since both this bar 

 and the connective plate (a) underlap the torma, the anterior part 

 of the latter appears to be sunk into the lower wall of the labrum. 

 Posteriorly a strong apodeme (Ap) arises from the dorsal surface of 

 the torma and curves mesally. On this apodeme are attached two 

 large muscles (mcls) from the frontal region of the head. Con- 

 traction of the muscles evidently rocks the torma mesally on its 

 articular points and thus gives a backward and mesal stroke to the 

 connected brush. The reverse movement of the brush, as other writers 

 have noted, results from the elasticity of its basal connections. Ac- 

 cording to Cook (1944a) in specimens of Theobaldia [Culiseta] 

 killed and fixed with the brushes retracted, on cutting the muscles 

 the brushes quickly spring back to the expanded condition. 



The Aedes tormal mechanism is probably characteristic of the 

 Culicinae. The same structure and musculature is shown to be present 

 in Culex by Thompson (1905) and by Chaudonneret (1951), and in 



