NO. 8 ANATOMICAL LIFE OF THE MOSQUITO — SNODGRASS 2T 



fore, do not identify the head area on which they arise as any part 

 of the labium. 



The interpretation of these parts has been still further confused by 

 Shalaby (i957d), who regards the median ventral head area as the 

 labial submentum and mentum, the toothed hypostomial lobe as the 

 paraglossa, the fringed lobe below it the glossa, and the entire complex 

 above the toothed lobe the hypopharynx. Comparative studies, as 

 already shown, give no basis for any such interpretation. Moreover, 

 the adult labium is formed entirely from the rudiment beneath the 

 cuticle of the larval labium (figs. 9 F, 15 A, pLb) and involves no 

 part of the ventral head wall of the larva. 



The larval labiohypopharynx is evidently retractile, but it plays no 

 active part in feeding. Its principal function is said to be that of 

 an "anvil" on which the incisor points of the mandibles strike to break 

 up food particles. 



Elaborate studies of the developmental changes in the mouth parts 

 of larval instars of Anopheles, Aedes, Culex, and Psorophora have 

 been made by Shalaby (1956, 1957a, 1957b, 1957c). 



The pharynx. — The pharynx of larvae that feed on water-borne 

 particles is a small, flattened, ovate or heart-shaped, thin-walled sac 

 (fig. 8 C, Phy) opening directly from the wide mouth (fig. 7 B, Mth) 

 and tilted upward and posteriorly in the head. From its posterior 

 ventral surface is continued the thick-walled oesophagus (fig. 8 C, 

 Oe). The ventral wall has an outer layer of semicircular muscles 

 (E, cmcl) the dorsal wall is crossed by four wide muscle bands (C, 

 tmcl) ; the extrinsic musculature includes dorsal and ventral dilator 

 muscles from the head wall. The lateral margins of the pharynx are 

 strengthened by two narrow, concentric, riblike thickenings on each 

 side, convergent to the narrowed posterior end. Internally each of 

 these ribs bears a long brush of fine hairs (D), suggestive of the 

 brushes in the mouth of a baleen whale, and in fact they serve the 

 same purpose, namely, that of filtering the food matter from the in- 

 gested water. A pharyngeal filter apparatus very similar to that of 

 the mosquito larva is shown by Anthon (1943a) to be present in the 

 larvae of several other nematocerous families. The pharynx of the 

 predaceous culicid larva of Toxorhynchites, however, is a simple 

 funnnel-shaped enlargement of the anterior end of the oesophagus, 

 and has no filter brushes. In any case, the larval pharynx is not to be 

 identified with the sucking pharynx of the adult mosquito, which lies 

 in the posterior part of the head (fig. 24 A, PhP), and the larva has 

 no cibarial pump. 



