412 Transactions of the Society. 



than in other orders, and the fine black granule already alluded to, 

 is present in the very large majority of cases. 



In the Culicidai, Tabanidse, Glossinidse, and Stomoxidre, that are 

 known blood-suckers, and whose mouth-parts are so modified that 

 it is scarcely possible for them to obtain other food, that food, 

 when digested, presents a certain character, rather like that of 

 albumen, cracked and shrivelled up, and resembles in some degree 

 that seen in Vespa. I found a similar appearance in one of my 

 preparations of the house-fly (Musca domestica L.) caught inside the 

 house, and concluded that she (it was a female) had been sucking 

 the juices of ra\\ r meat, a highly probable occurrence. The pollen- 

 feeders present no difficulties ; their food is mostly undigested, the 

 insects being caught on the flowers, and sometimes the plant on 

 which the insect was feeding can be recognised by the characters 

 of the pollen. 



There is a group consisting of such flies as the house-fly, the 

 blow-fly (Calliphora erithrocephala Mg.), and the green bottle-fly 

 (Lucilia), which seem to feed on anything and everything, and the 

 contents of their abdomens are baffling. 



Eepeatedly in certain flies, mostly inhabitants of fields or 

 gardens, in the midst of the amorphous mass of digested food, 

 little dark brown, semi-transparent, cellular organisms are seen. 

 These, from a comparison with plates and descriptions, I should 

 think are the spores of some of the " rusts " or " mildews." 



Owing to the small size of the openings in the mouth, no 

 large fragments can reach the stomach ; I have, however, four 



EXPLANATION OF PLATE VIII. 



Fig. 23. — Trophi of Empis livida L. 9 . The mouth-parts do not differ, and 

 both sexes are predaceous. To illustrate Rule 2. Lateral view. 



Fig. 24. — Trophi of Platychirus manicatus Mg. $ . The mouth does not differ 

 in the sexes. A pollen feeder, like all the Syrphidce. To illustrate Rule 3. 

 Lateral view. 



Fig. 25. — Trophi of Helomyza rufa Fin. 9 . The mouth does not differ in the 

 sexes. This insect is placed in the somewhat anomalous group of Heliomyzidae, 

 and is only representative of the flower feeders, and illustrative of Rule 4 as 

 regards itself ; some species of the genus differ in type. Dorsal view, and rather 

 diagrarnmatically drawn. 



Fig. 26. — Trophi of Conops quadrifasciata Deg. <J . The mouth does not differ 

 in the sexes. The labium, chiefly by a modification of the mentum, has under- 

 gone changes, which have made it into a hard style, fitted to probe the nectaries 

 and cavities of flowers. To illustrate Rule 7, and for comparison with Fig. 20 

 (Lyperosa), which has undergone similar changes. Lateral view. 



Fig. 27. — Labrum of Pcecilobothrus nobilitatus L. 9 . Dorsal view. 



Fig. 28. — Labrum of P. nobilitatus 9 . Lateral view. 



Fig. 29. — Hypopharynx of P. nobilitatus 9 . The mouth-parts do not differ 

 in the sexes. Pcecilobothrus is a genus of the Dolichopodidse, is predaceous, 

 and is often seen on shallow brooks and streams, skating on the surface film. 

 To illustrate Rule 9. Dorsal view. 



Fig. 30. — Labrum of Phora incrassata Mg. 9 . This part is quite simple in 

 the male, and without the sharp processes. To illustrate Rule 9. Dorsal view. 



