52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



larva in that it is completely closed from the occipital foramen to the 

 base of the proboscis. The head is attached to the thorax by a slender 

 membranous neck and is supported by a pair of lateral cervical sclerites 

 (D,E). The head of the male is similar to that of the female, but 

 is a little smaller. The internal head skeleton consists of a pair of 

 simple tentorial arms extending from anterior pits above the lateral 

 angles of the clypeus (A, at) to posterior pits (B, pt) on the ventral 

 margin of the occipital foramen. 



From the front of the face arise the long antennae (fig. 2oD,E). 

 The hairy flagellum of each organ is borne on a large globose base 

 (A, Pdc), which is the pedicel, or so-called torus, but when the pedicel 

 is removed (right) it is seen to be itself supported on a narrow ring 

 (Sep) that represents the usually much longer scape of other insects. 

 The slender shaft of the flagellum is divided into 14 sections (errone- 

 ously called "segments"), 13 of which carry each a whorl of hairs. 

 In general the sexes are readily distinguished by the number and 

 length of the flagellar hairs, which in the male (fig. 22 A) give the 

 antennae a plumose appearance in contrast to the short-haired female 

 antennae (D,E). The two types, however, intergrade, females of 

 some species having bushy antennae, and some males short-haired 

 antennae. In the female the hairs arise from clear areas near the bases 

 of the flagellar units (B) ; in the male (C) they are borne on promi- 

 nent, darkly sclerotized, subapical expansions of the units. Tulloch 

 and Shapiro (1951) have shown from electron microscope studies that 

 the flagellar hairs are armed with rows of minute teeth; in Culex 

 quinquefasciatus they estimate there are at least 16 rows along each 

 hair. These writers, however, are in error where they say the hairs 

 "arise at the junctions of the flagellar segments." 



The large globose pedicel of the antenna in each sex contains a 

 highly developed sclopophorous sense organ, present also, though 

 usually much smaller, in the antennal pedicel of most insects. The 

 organ was first described in Culex as an auditory organ by Johnston 

 (1855), who did not at all understand the nature of the structure in 

 the pedicel, but it has since been known as Johnston's organ. Sub- 

 sequently Child (1894) made good histological studies of the organ 

 in various insects, including the mosquito, and his illustrations are 

 now famliar in most entomological texts. A more recent comparative 

 study of the organ in Culex, Aedes, and Anopheles is given by Risler 

 ( I 955)- The component sensory elements in the pedicel are attached 

 to a plate or prongs on the base of the flagellum, and thus evidently 

 register movements of the flagellum. 



