MR. TUFFEN WEST ON THE FOOT OF THE FLY. 



405 



to their extremities; tlie expanded parts are extremely attemiated, so much so as to 

 require a high power and obHque light to make them out. These insects (not being 

 aquatic) also secrete a fluid for the same purpose as the Fly : and I can imagme that if, 

 after the ends have been attached and moistened, these folds could be ptxt upon the stretch, 

 thereby lengthening the tubes, and consequently having a tendency to produce a vacuum, 

 they would form an excellent apparatus for attachment." 



There must be some mistake here; hak-like organs of this kind, loith corrugations, 

 are (I believe, as the result of numerous observations) only present on the tarsi of those 

 beetles which possess them for sexual purposes. Misled by preconceived ideas, although 

 the correct term was applied to the appearance presented, a hypothesis is started to ac- 

 count for it, of which the least that can be said is that it is quite inconsistent with the 

 structure of the parts concerned. 



Gosse (1859)* describes the " strong divergent hooks " of the Fly's foot as being them- 

 selves well clothed with spines t ; the difference in outline of the flaps in different species 

 of flies ; their being " thin, membranous, and transparent," so that " when a strong light is 



reflected through them " " their structure is seen very distinctly." The appearance 



of " lozenge-shaped areas " on " the inferior surface of the palm " is also mentioned, and a 

 conjecture is started as to their real nature. " From the centre of each area proceeds a very 

 slender, soft, and flexible peUucid filament, which reaches downwards to the surface on 

 which the fly is walking and is there slightly hooked and enlarged into a minute fleshy 

 bulb. Those from the areas near and at the palms arch more and more outwards, so that 

 the space covered by the bulbs of the filaments is considerably greater than that of the 

 palm itself. Now it is evident that the bulbous extremities of these filaments are the 

 organs of adhesion. We notice how they di-ag and hold, as the fly draws its foot from its 

 place ;" the marks left on the glass by these " filaments " when " the foot is suddenly 

 removed" are supposed to show "that the adhesion is effected by means of a glutinous 

 secretion poui^ed out in minute quantities from these fleshy tips." The necessary vitiation 

 of the results when an insect is confined in a " nearly air-tight glass cell" is observed 

 upon with a view to caution agamst building too much upon them. As already stated, 

 however, the experiment is easily repeated witli flies mo\ang on plane glass surfaces, 

 where errors from this cause cannot arise. 



The inquiry is extended to the "similar appendages" on the "joints of the foot" of 

 some Beetles. Timarcha tenebricosa is adduced as the first example ; unfortunately the 

 specialization of structure of these holding appendages is not well marked on the tarsi of 

 this insect, though the «' velvety cushion of a rusty-brown colour," is present, and very 

 dense. The outline of the joints composing the tarsus is then mentioned; with the 

 absence of cushioned soles from the last, which "carries two stout hooks." "The first 

 three" are described as "flat or even hollowed beneath into soles, something like the hoof 

 of a horse ;" an excellent comparison, wliich may be extended even to the structure itself. 

 It is only necessary to imagine the parts cemented together by an elastic material to have 



* Evenings at the Microscope, pp. 131-143. 



t See also Inman, p. 8, who considered this appearance of being "imbricated or covered with scales " to be owing 

 to the claw having "its formation originally by cells." 



3i2 



