410 MR. TUFFEN WEST ON THE FOOT OF THE FLY. 



near its end, when it suddenly bends downwards. Here tlie actual cavity ceases, and the 

 shaft assumes a mechanical texture, such as would be capable of transmitting minute 

 quantities of fluid by exosmosis ; its form now becomes altered into that of a broad thin 

 blade, and its direction again suddenly changed to a horizontal one, as it expands into 



2. A verj thin, elastic membranous expansion, perfectly smooth on its under surface, 

 with faint radiating lines in its substance, capable of adjustment to a smooth, flat, or 

 slightly undulating surface, on which, when pressed, it will take firm hold. 



It became desirable to endeavour to ascertain how far the structure of these append- 

 ages, which I have called teuent hairs, agrees with that of true hairs, on which some 

 valuable critical observations were made last year by Dr. Hicks *. His remarks cannot 

 be improved upon ; so I quote them entire. He is discussing some " peculiar modifica- 

 tions of true hairs," "not processes of the ctiticle." 



"It is requisite to bear in mind the true nature of the hair in Insects — namely, that it 

 is situated in a depression caused by the absence of the inner layers of the integument, 

 into which the cuticle is continued. In the centre of this cuticular depression a small 

 elevation or papilla arises, which is the true root of the hair, which rises from it of 

 various length. By means of this arrangement, the hair itself is capable of some degree 

 of motion. The interior of the root of each hair is in connexion with the internal parts 

 of the member on which it is situated ; commonly fibres run to it, probably always in- 

 eluding a branch of a nerve ; and this is decidedly the case in those hairs situated near 

 the prominent parts and extremities of the various members, as, for instance, the tips of 

 the antennai, the palpi, pads of tarsi, &c. ; and this branch of the nerve does not run into 

 the interior of the hair, but only to the inner aspect of the root, which separates it 

 entirely from the interior. The difference between this structure (true hairs) and cuti- 

 cular processes must be particularly borne in mind : the latter, having no root, and not 

 being situated in a dej)ression, evidently only spring from the surface. The spine must 

 also be distinctly separated from the true hair, being a tapering process of the whole in- 

 tegument, into the interior of which the contents of the body can freely pass f." 



With these clear indications for a guide, it was not difficult to ascertain, by carefully 

 making very thin sections, that the tenent hairs agreed in their structure with the cha- 

 racters of true hairs as defined by Dr. Hicks : sections of some of the undoubted hairs 

 on the lateral margins of the tarsal joints, obtained at the same time, were found to 

 agree in structure. This proved the correctness of Dr. Hicks's observations on the struc- 

 ture of true Insect hairs ; and, at the same time, it proved also that tenent hairs must be 

 classed in the same category. 



These facts arc illustrated in sections from Carahits (fig. 21, PI. XLII.). 



* Trans. Linn. Soc. vol. xxiii. part i. p. 143. 



•j- The facts of the case could not be better put ; yet it must always be borne in mind that all organized structures 

 are formed out of the same tissue, and that the differences they present are due solely to a greater or less amount of 

 differentiation of that tissue. On the Cricket's leg are spines which show at their bases of attachment the earliest in- 

 dications of that kind of differentiation which is characteristic of true hairs. So also the calcaria, which are, when 

 greatly developed, very moveable, probably possess muscles and nerves, and in some cases have a membranous sucker- 

 like expansion at their ends — modifications of true hairs : in many other insects they are simply spinous continuations 

 of the tibia. 



