6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



head. The part of the head wall cut out at ecdysis may be termed the 

 cephalic apotome (F, Apt). 



The space between the arms of the cleavage lines and the 

 clypeolabral sulcus in the mosquito larva has been variously called the 

 "frons," the "clypeus," and the "frontoclypeus." The respective areas 

 of the frons and the clypeus may be identified in other insects by 

 specific groups of muscles that arise on them. In the mosquito larva 

 the clypeal muscles arise anteriorly, the frontal muscles posteriorly on 

 the central head area, but there is no external demarcation between 

 the two regions. This area, therefore, is frontoclypeal in a limited 

 sense, but it is not the entire clypeus or the entire frons. Ordinarily 

 the clypeus extends laterally to the bases of the mandible, and in adult 

 insects the frons is the facial area between the antennae and the eyes. 

 The whole aspect of the mosquito head is changed at the transfor- 

 mation to the pupa and the adult. 



The larval antennae are slender, unsegmented shafts bearing vari- 

 ously distributed spines and tufts of long hairs. Each terminates in 

 a small apical papilla. The antenna of the pupa, being eventually much 

 larger than the larval organ, does not develop within the latter but in 

 a pocket extending posteriorly from the base of the larval antenna. 



The eyes of the larva are each a group of simple lateral eyes ; their 

 structure in Culex pipiens has been described by Constantineanu 

 (1930) and by Sato (1951b). According to Sato each eye consists 

 of three parts, each with its own retinular cells. One part is central 

 and has three retinulae, a second part is dorsal and has a single retinula 

 of eight cells, the third part is a long band of about 40 cells surround- 

 ing the other two parts dorsally, anteriorly, and ventrally. Con- 

 stantineanu, on the other hand, describes five parts in the eye of Culex, 

 as in some other nematocerous larva. Probably the three retinulae of 

 Sato's "central part" are regarded as three eyes. The larval eyes 

 have no lenses, the ordinary head cuticle being continuous over them. 

 They are present from the beginning of the larval stage and persist 

 into the pupa, or even into the adult. 



The presence of large, darkly pigmented compound eyes visible on 

 the surface of the head gives the mosquito larva, as also the corethrid 

 larva, a very unusual appearance. The compound eyes of other re- 

 lated Nematocera are developed likewise in the larva, but, because of 

 the absence of pigment until the pupa stage, they are not apparent ex- 

 ternally. 



The undersurface of the larval head (fig. 3 C,D,E,F) is more dif- 

 ficult to understand than the upper surface. The mandibles and 



