414 Transactions of the Society. 



dorsal or upper part of the proboscis. This is explained by the 

 assumption, that palpi situated on the lower portion of the pro- 

 boscis, would in the process of evolution work round to the upper, 

 if advantage were gained by doing so. A parallel case is the well 

 known one of the eye in the flat fishes, which works round from 

 a symmetrical to an asymmetrical position on the ur»per side, 

 during the transition from the young to the adult stage.* 



It remains to describe these mouth-parts of Muscidse that are 

 provided with two palpi in addition to those always present and 

 generally called maxillary. 



In several species of the Anthomyia family, in the genera 

 Hyetodesia, Spilogaster, and Hydrotea, are to be found at the base 

 of the labrum and hypopharynx, and connected with the apodemes 

 or levers that work those parts, two hairy processes, one on each 

 apodeme.t These are jointless, chitinous in structure, thickly 

 haired, and have much the appearance of ordinary palpi, fig. 6. 



In Hyetodesia basalis 9 they are very well marked, but are 

 shorter in proportion to their breadth than in Spilogaster dupli- 

 cata 9 and S. flagripes ? (?), fig. 7. 



In H basalis they measure ^-^ in. in length C • 084667 mm.), 

 while in Spilogaster duplicata, which is a smaller fly, they are the 

 same length and about half the breadth. 



Even in these insects, the organs may be considered rudi- 

 mentary, but there are many species where only a few hairs on a 

 minute tubercle remain. Such rudiments may be found on Lasiops 

 ctenoctema i 9 , Anthomyia radicum 6 9 , Phorbia jloccosa s (very 

 small), Pegomyia bicolor $ ?, Homalomyia canicularis S 9 (very 

 small), Hylemyia strigosa 6 , and Azelea macquarti s . 



In the Sarcophagidse rudiments may be found in Myiocera 

 carinifrons, and in Musca corvina and M. domcstica of the Muscidse, 

 so the rudimentary palpi are not restricted to the Anthomyia 

 section of the Muscidae, fig. 5. 



I first noticed these organs on a slide of Spilogaster duplicata, 

 cleared, mounted under pressure, and with a magnification of over 

 300 diameters. I have also seen them with an ordinary simple 

 lens on the proboscis of Hyetodesia perdita, a rather large fly, 

 about 10 mm. long, fig. 8. If a newly killed fly of this species 

 be procured, the proboscis taken hold of by a fine pair of forceps, 

 drawn out to its fullest length, and examined with a magnification 

 of 10 or 15 diameters, it will be seen that the labrum and hypo- 

 pharynx are lying flat, in the cavity of the labium hollowed out 

 for their reception, but the rudimentary palpi are not visible. 



It is obvious that if the hypopharynx is to be used, it must 

 rise from the cavity in the labium at a more or less acute angle 



* Darwin, Origin of Snecies, chap. vii. 



t The palpi have also been found in species in the families Sepsidse, Opomyzidse, 

 and Borboridse. 



