NO. I THE INSECT HEAD — SNODGRASS 31 



termed flagellomeres, as suggested by Imius (1940), but they are 

 not "antennal segments." 



Among adult Pterygota the antennae take on a great variety of 

 forms, produced chiefly by modifications of the flagelkmi, or by a 

 differentiation of its annuH. Typically the flagellum is slender and 

 cylindrical (fig. 14 B), but it may be club shaped, or extended as a 

 long, tapering filament. In the lamellicorn beetles some of the distal 

 annuli are produced at right angles to the shaft as overlapping leaf- 

 like plates (C). A particularly specialized type of antenna is that of 

 the muscoid flies. The first annulus of the flagellum has a tendency to 

 be larger than the others (B, D). The enlargement is much exagger- 

 ated in a tabanid fly (E, ifl). In the muscoid antenna (F, G) this 

 flagellomere becomes a large oval lobe {ifi) borne on the pedicel, and 

 the rest of the flagellum is reduced to an arista (Ar) consisting of two 

 small basal annuli, and a long, tapering, simple or usually branched 

 distal shaft. 



The antennae of holometabolous larvae are often so different from 

 those of the adult that they appear to be special larval organs rather 

 than developmental stages of the adult antennae. It is principally 

 among the Neuroptera that the larval antennae resemble adult an- 

 tennae in having a multiannulate flagellum (fig. 15 A), though in 

 many species they are reduced to three small units. Antennae 

 of four or five units occur in the Megaloptera (B) and in Can- 

 tharidae, Dytiscidae, and Hydrophilidae among the Coleoptera, but 

 the antennae of most larval beetles are very small, three-segmented 

 organs (F). Similarly the antennae of lepidopterous larvae (D) 

 have only three segments, the third being a mere apical lobe on the 

 second (E). Among the nematocerous Diptera the larval antennae 

 are always short, but are variable. In Chironomus the antenna (C) 

 may have three short apical units on a long base, but in the mosquito 

 larva the very small antenna (G) is undivided. In the higher 

 Hymenoptera the larval antennae are represented by only slight 

 swellings or mere discs of the head wall. In the muscoid fly larva the 

 antennae are entirely eliminated externally, being formed in a pair 

 of long sacs from the frontal region of the head that extend back 

 into the thorax. 



When the larval antenna is greatly reduced in size, the succeeding 

 pupal antenna develops either beneath the cuticle of the head, or 

 more commonly in a pocket of the epidermis beneath the larval an- 

 tenna, usually with its tip in the latter. In the mosquito, for ex- 

 ample, as shown by Imms (1908) the pupal antenna is formed in a 

 deep pocket of the head, but has no connection with the larval organ. 



