66 



COXXECTICUT GEOL. AXD XAT. HIST. SURVEY [Bull. 



1923) formerly considered that the lobe-like pulvilliform empodium, 

 ar, of the Tabanidae (Fig. 8, L) etc., represents an aroliiim, because 

 it extends dorsallv to the unguifer, or claw-bearmg process of the dis- 

 titarsiis, while the setiform empodium {em, of Fig. 8, K) of the Asil- 

 idae, etc., is a true empodium. because it appears to be a process of 

 the uno-uitractor plate, u^ and does not extend dorsalh^ to the unguifer. 

 HohNifv, 1937, (M. S. C. doctor's thesis on the "Pretarsus of Insects"), 

 however, agrees with Ockler (1800) and the dipterists hi general, who 

 consider' that the setiform empodium {em of Fig. 8, K) and the pul- 

 villiform empodium {ar of Fig. 8, L) are homologous structures, and 

 supports the view of de Meijere (1901), who considers that the entire 

 arolium of the Tipulidae and Trichoceridae is not strictly homologous 

 witli the pulvilliform empodium of the Tabanidae {ar of Fig. 8, L). 



According to Holway, 1937, (1. c.) the arolium, such as that oc- 

 curring in the Tipulidae, Trichoceridae, etc., is a median sac-like out- 

 pouching of the acropod (pretarsus) which includes a dorsal region, 

 typically membranous (although it may contain sclerotized areas), and 

 a ventral plantar area, from which an empodium of the pulvilliform 

 or setiform type may develop ; and the setiform empodium appears to 

 be a process of the unguitractor plate when the membrane between 

 the ])lantar area and the unguitractor becomes sclerotized to form a 

 continuous surface extending from the unguitractor plate into the em- 

 podium. 



In the acropod (pretarsus) of the Simuliidae, a dorsal unpaired 

 median lobe is folded over the ventral setiform empodium, and Hol- 

 way interprets the dorsal lobe as the dorsal region of the arolium, in 

 which the ventral plantar area has developed into a setiform empo- 

 dium, although in most Diptera the dorsal arolear membrane becomes ^ 

 reduced, when the ventral plantar area develops into an empodium of ' 

 the setiform or pulvilliform type. 



A pulvilliform empodium is developed in certain Ptychopteridae, { 

 Anisopodidae, Mycetophilidae, etc., among the Nematocera, in which 

 the pulvilli or lateral pads at the bases of the claws {pv of Fig. 8, L) 

 are usually not developed. In some species of &ciara^ however, a i 

 small pulvillus occurs on each side of the pulvilliform empodium; 

 and in such bibionids as Bibio^ Aspistes, etc., well developed pulvilli 

 flank the pulvilliform em[)odiiim, as is also the case in the brachyc- 

 erous families Leptidae, Stratiomyidae, Tabanidae (Fig. 8, L), etc. 



An empodium of the setiform type may occur in such Nematocera 

 as the Chironomidae and Culicidae,"but it is not flanked by pulvilli in 

 the Culicidae. A setiform empodium usually flanked by pulvilli (al-; 

 though the pulvilli may become slender and elongated in such forms 

 as the Asilidae, Mydaidae, etc.) occurs in the brachycerous families 

 Therevidae, Mj^daidae, Asilidae, Bombyliidae, Cyrtidae, Empidae, 

 Dohchopodidae, etc., and such a setiform empodium flanked bv pul- 

 villi IS typical of most Cyclorrhapha. The setiform empodium of the 

 hippoboscid shown in Fig. 8, E, is rather broad, and in such Diptera 

 as certain Asilidae, Cyrtidae, Dohchopodidae and Empidae, the seti- 

 form empodium may become markedly widened basally; and such 

 typeb of empodium, acccu-ding to Holway, 1937, (I.e.) represent in- 



