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4 18 MR. TUFFEN WEST ON THE FOOT OF THE FLY. 
by slight viscidity of the fluid, by the action I have so often alluded to, which may he 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 Tipulidce, 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 
b 
with, really goes to prove the universality of the rule. 
It occurs in an example of the aberrant family Hippoboscidce ; the species I have not 
yet determined. Here at first sight there appeared to be no pulvilli at all at the end of 
the tarsi (the typical Coleopterous foot). But more careful examination revealed two 
minute rudiments of a pulvillus. 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 
pulvillus 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 a 
their tips, and have no membranous expansions (fig. 18, PL XLL). In another species, 
belonging to the same family, the pulvillus is present, very thin, narrow, and deep } 
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 Sargus in my possession is interesting in more than one respect (ng. » 
PL XLL). Thepulvillus is trilobate ; the central lobe the largest and subtriangular, with 
the base distal ; the lateral lobes are also subtriangular, but with their bases proxmia L 
Prom the central lobe arises a comparatively small number of tenent hairs, which are muc 
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. Prom the base of the fifth tarsal joint arise 11 long, 
overarching setae (guard-hairs), which bend downwards towards their points. The cafl 
have scales at their bases, and are sharply pointed and abruptly curved towards 
free end like Chamois-horns. 
The only example which has occurred to me of a foot formed on the Dipterous yp 
not belonging to that natural order, was in an Acarus, of undetermined species, 
which I believe to be a Zeptus or Trombidium. This had an uncleft pulvillus* m 
Dipterous-like tenent hairs ; the robust ungues were furnished with several long tac 
hairs on their under surface, as occurs on the same part in many of the Hymenop 
(fig. 73, PI. XLIIL). 
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