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TEXT-BOOK OF ENTOMOLOGY 



face; in this adhesion they are aided by the secreted fluid." In 

 the case of the Diptera he does not accept the theory by which the 

 movement of the fly along smooth surfaces is ascribed to an alternate 

 fixation and separation, but believes in a process of adhesion, aided 

 by a secretion, as in many Coleoptera. (In the Cerambycidae there is 

 no secretion, and the tubules are merely sucking organs, like those 

 observed in the male Silphidae.) " The attaching lobes, closely beset 



with chitinous hairs, are 

 enabled, in consequence of 

 the pressure of the foot, to 

 completely lie along any 

 smooth surface ; this expels 

 the air beneath the lobes, 

 which are then acted on by 

 the pressure of the outer 

 air." (Journ. Roy. Micr. 

 Soc., 1884, p. 736.) Another 

 writer (Rombouts) thinks 

 this power is due to capil- 

 lary adhesion. 



The action of the pul- 

 villus and claws when at 

 rest or in use by the honey- 

 bee is well shown by Chesh- 

 ire (Fig. 135, 5). In as- 

 cending a rough surface, 

 "the points of the claws 

 catch (as at B) and the 

 pulvillus is saved from any 

 contact, but if the surface 

 be smooth, so that the 

 claws get no grip, they 

 slide back and are drawn 

 beneath the foot (as at ^4), 

 which change of position 

 applies the pulvillus, so that it immediately clings. It is the 

 character of the surface, then, and not the will of the bee, that 

 determines whether claw or pulvillus shall be used in sustaining it. 

 But another contrivance, equally beautiful, remains to be noticed. 

 The pulvillus is carried folded in the middle (as at (7, Fig. 105), but 

 opens out when applied to a surface ; for it has at its upper part 

 an elastic and curved rod (cr, Figs. 105 and 135), which straightens 



FIG. 132. Fore leg of tf Dyticus, under side, with 

 sucker, formed of 3 enlarged tarsal joints : with a small 

 cuiiule highly magnified, x 120. After Miall. 



