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which is as yet undescribed. The specimens have got a little spoilt by the medium in 
which they are mounted, but they still show a pair of organs beneath some of the finely 
pectinate much bent ungues, which represent either a pair of tenent hairs or a rudi- 
mentary imlvillus. This can hardly be determined without further specimens, in better 
condition ; but in any light the structure is interesting as being unique, so far as I am 
at present aware, amongst marine Articulata. 
Tenent hairs are so usually present in some modification or other, that it is really 
difficult to name a beetle which has not some form of them ; the only one I yet know, 
that seems to me really to possess nothing of the kind, is a species of Helops, which lives 
on sandy heaths ; I suppose the dense cushion of hairs on the tarsi here to be for the 
protection, simply, of the joints to which they are attached. I have detected them on the 
tarsal joints of species of Ephydra, and on the first basal tarsal joint of the Drone of the 
Hive-bee. A very rudimentary form of tenent hairs is present on the under surface of some 
of the Tree-bugs (Pentatomidse), which have, in addition, a large deeply cleft organ at 
the extremity of the tarsus, which appears to be a true sucker, and will be afterwards 
described. 
To return now to our first subject, the Fly's foot. 
I do not see that it is necessary to add much to the observations which have been already 
made, or which will have suggested themselves, on the action of the parts of which it is 
composed. 
"When a Fly is not making use of its pulvilli, as on a surface sufficiently rough to afford 
it foot-hold with its claws alone, these only are made use of, — remembering of course what 
has been already said on the greatly increased hold gained by parts mutually opposed 
drawing towards each other. When walking on such a surface, the foot represents that 
of a Coleopterous insect without any tenent appendages. 
On a smooth surface, perpendicular or horizontal, the pulvilli are brought down, and 
the tenent hairs applied to such surface : a slight push forwards of these, succeeded by a 
gentle draw backwards, at each application, removes the air between their soft, elastic 
expansions and then plane of motion, and thus a firm hold is gained. Access of air is 
prevented by the minute quantity of moisture which exudes from the expanded tips of the 
tenent appendages; and thus a vacuum is formed, on the same principle as in the 
"Atmosperic Hat-peg," the "Plate-holder" of the Photographer, or the " Artificial 
3 
Gums " of the Dentist. When the Ply wishes to move a leg from its place of attachment, 
the claws are brought down and pressed against the surface ; from their position they 
raise the hinder part of the pulvillus, where the tenent hairs are least developed, first, 
and so on forwards. If the claws were attached to the fifth joint, as it has been supposed, 
they could not act equally well in the way I have mentioned ; and I think a fly when 
once stuck fast, if it had no claws, might remain so * 
This introduces the curious question, " What is the pulvillus of a Ply ? 
J> 
The analog}" 
between this part and the bilobed joints of some of the beetles has been noticed by previous 
observers f ; it will readily suggest itself on a reference to the figures given in illustration 
of the present paper. 
* See also Tyrrell and Lister, loc. cit. 
t Westwood ; Inman ; passim 
