'No. 0)4] DIPTERA OF CONNECTICUT: MORPHOLOGY 35 



the labial palpi, la of Fig. 2, J, as it does in the more primitive forms 

 (Fig. 2, E), while the true mentum never bears the palpi in this fash- 

 ion, and there can be little doubt that the sclerite here designated as 

 the prementum in the Diptera is homologous with the prementum of 

 the lower forms. 



The prementum, pm, is a well developed plate in Bittacotnorpha 

 (Fig. 2, A), and forms the principal sclerite of the proboscis of the 

 higher Diptera (Fig. 2, G; Fig. 4, A, E and B). It is the portion of 

 the labium which becomes elongated in the mosquito (Fig. 3, E), and 

 the prementum is also greatly elongated in the cyrtid shown in Fig. 

 3, C, as well as in such tabanids as Pangonia longirostrls, etc. The 

 prementum is usually called the theca by dipterists, although Hendel 

 (1928) also applies the term theca to the hyoid sclerite. The crmnena 

 of scale insects is also called the theca, and the basal region of the 

 aedeagus of the male, in the higher Diptera, is likewise called the 

 theca, while in the caddice worms this term is applied to the case 

 carried by the larva, and the term theca is also applied to the outer 

 covering of pujDal insects and various other structures, so that it is 

 preferable to apply the designation prementum (instead of "theca") 

 to the sclerite in the Diptera which is homologous with the premen- 

 tum of other insects in general. 



The labella, la, of the lower Diptera are the slender, two-seg- 

 mented structures borne on the distal ends of the halves of the pre- 

 mentum, pTn, (Fig. 2, J), exactly as is the case with the slender, two- 

 segmented labial palpi of the Mecoptera shown in Fig. 2, E and I. In 

 the pupa of the primitive tanyderid Protoplasa, the labella arise ex- 

 actly as the labial palpi do in the pupae of the Lepidoptera (compare 

 Fig. 3 with Fig. 4 of Plate 3 of paper by Crampton, 1930), in which 

 no one disputes that the structures in question are the labial palpi, so 

 that it is difficult to understand how anyone could mistake the labial 

 palpi of the Diptera for paraglossae, and other structures with which 

 they have been homologized by diiferent investigators. The labella 

 frequently bear labellar processes, or labellar lobes, Ip, in the low^er 

 Diptera (Fig. 2, C, D and J), and these lobes are interpreted as the 

 "glossae" by Peterson (1916), MacGillivray (1923), and others who 

 consider that the labella represent the paraglossae of the labium. 



The basal segment (basilabellum) of the labella, hi, may be longer 

 than the distal segment, dl, (distilabellum) in such primitive blepha- 

 rocerids as Edwardsm-a (Fig. 2, J — compare also Fig. 2,1), in which 

 the slender, two-segmented labial palpi are distinctly separated; but 

 the distal segments usually develop at the expense of the basal ones, 

 and become lobe-like structures, which are connected basally, and are 

 known as the oral lobes in the higher Diptera. The labella are long 

 and slender in such Nematocera as the tipulid Geranamtjia (Fig. 4, H) 

 and in the blepharocerid shown in Fig. 3, D ; and Edwards (1931) has 

 described a chironomid, Rhinocladius longirostrls, in which the labella 

 are as long as the entire body — which is probably a record for the 

 Diptera. In the empid Empis clausa, the labella are slender and elon- 

 gated, but in the higher Diptera they are usually broad lobes. In the 

 stable fly Stomoxys, 2ind in Glossina, and also in the hippoboscids, the 



