52 HUMBLE CREATURES. 



(same figure), resemble the broad termination of a 

 child's battledore formed of parchment. Until re- 

 cently, these pnlvilli, which are furnished with innu- 

 merable hairs, were supposed to operate as suckers ; 

 but the higher powers of the microscope have revealed, 

 at the termination of each of the numerous hairs that 

 cover the surface, a minute expansion, which is kept 

 moist by a fluid exuding from the extremity*; and 

 the belief now prevails that, whilst each single hairlet 

 (PI. VII. fig. 1, o) serves as a sucking disc, the two 

 pulvilli themselves act as cushions for the preserva- 

 tion of the larger hooks (which would otherwise 

 become abraded), in a similar manner to the soft 

 cushions that protect the sole of a cat's foot, and 

 enable it to tread so lightly. 



This view is strengthened by the examination of 

 the foot of Dytiscits marginalis, one of the large 

 Water-beetles, in which these small suckers are deve- 

 loped in a remarkable degree ; and also to some extent 

 by the ambulacral suckers that serve as members of 

 locomotion in the Star-fishes and other Echinoderms, 

 and the terminal cushions upon the toes of the ClLmb- 

 ing-frog {Hyla arborea), in all of which a power is 

 imparted similar to that possessed by the House-fly. 



With this description of the Fly's foot, we shall 

 conclude our cursory review of its external parts; 

 and, before quitting this portion of the subject, let us 



* For this discovery we are indebted to Mr. Hepwortli : see 

 his paper in the Quarterly Journal of Microscopical Science, 

 1854, vol. ii. p. 158. 



