418 MR. TUFFEN WEST ON THE FOOT OF THE FLY, 



by sliglit viscidity of tlie fluid, by the action I have so often alluded to, which may be called 

 "grasping," by molecular attraction, and, doubtless, by other agents still more subtle, 

 with which we have at present scarcely any acquaintance. 



The Orders of Insects have, for the most part, each their own type of foot. Thus there 

 is the Coleopterous type, the Hymenopterous type, the Dipterous type, the Homopte- 

 rous type, &c. &c. : and these types are very distinctive, so that in critical instances they 

 will sometimes serve at once to show to which Order an Insect should be referred. Thus, 

 amongst all the Diptera, I have as yet met with but one subdivision which presents an 

 exception to the structure already described and figured. This exception is furnished by 

 the Tijndidce, which have the Hymenopterous foot. With hardly an exception, then, I 

 believe the form of foot described will be found universal amongst the Diptera, and will 

 be found amongst the members of this Order alone. One exception I thought I had met 

 with, really goes to prove the universality of the rule. 



It occurs in an example of the aberrant family IIl2)pobosciclcB ; the species I have not 

 yet determined. Here at first sight there appeared to be no p2ilviUi at all at the end of 

 the tarsi (the typical Coleopterous foot). But more careful examination revealed two 

 minute rudiments of a pulviUus. And the true state of the parts proved to be, that the 

 sixth tarsal joint was present, but in a most rudimentary condition, the part for holding 

 being cleft in twain ; these parts, membranous in their texture, apparently removed quite 

 away from each other, and soldered to the under surface of the fifth joint, near the roots 

 of the ungues : these claws, which are largely developed and very powerful, appear here 

 to be articulated unmistakeably to the fifth joint : the structure of the cleft rudimentary 

 piilvilliis at first sight presents nothing unusual in appearance ; but more careful examina- 

 tion shows that the hairs on its under surface are pointed, and apparently not soft at 

 their tips, and have no membranous expansions (fig. 18, PI. XLI.). In another species, 

 belonging to the same family, the pulvillus is present, very thin, narrow, and deeply 

 cleft, with minute tenent hairs of the Dipterous type : that the ungues have no connexion 

 with the fifth tarsal joint is admirably shown by this specimen (fig. 19). 



A foot of a Sargits in my possession is interesting in more than one respect (fig. 12, 

 PI. XLI.). Thepiihilliis is trilobate; the central lobe the largest and subtriangular, with 

 the base distal ; the lateral lobes are also subtriangular, but with their bases proximal. 

 From the central lobe arises a comparatively small number of tenent hairs, which are much 

 larger than those on the lateral lobes ; they are, in fact, the largest and strongest I have as 

 yet met with on any Dipterous foot. From the base of the fifth tarsal joint arise 11 long, 

 overarching setae (guard-hairs), which bend downwards towards their points. The claws 

 have scales at their bases, and are sharply pointed and abruptly curved towards their 

 free end like Chamois-horns. 



The only example which has occurred to me of a foot formed on the Dipterous type, 

 not lielonging to that natural order, was in an Accwus, of undetermined species, but 

 which I believe to be a Leptus or Trombidium. This had an uncleft xmlvillus, with 

 Dipterous-like tenent hairs ; the robust ungues were furnished with several long tactile 

 hairs on their under surface, as occurs on the same part in many of the Hymenoptera 

 (fig. 73, PI. XLIII.). 



