76 THE MICROSCOPE. 



and above them a pair of sharp hooks. On the. 

 interesting question alluded to above, I shall give you 

 what Mr. Lownes has lately written thereon. " The 

 foot-pads are amongst the most interesting parts of 

 the insect, because they enable it to walk upon 

 smooth surfaces in an inverted position, apparently 

 in defiance of the laws of gravity. Long ago this was 

 first ascribed, by Dr. Derham, to the exhaustion of 

 air from the foot-pads ; recently it has been supposed 

 to be due to the exhaustion of air from the extremities 

 of the hairs with which the pad is closed; others 

 have ascribed it to the hold which these minute hairs 

 take of trifling irregularities of surface; but none of 

 these explanations are correct, and one of the earliest 

 notions upon the subject is the nearest to the truth 

 that is, that the feet secrete a glutinous fluid which 

 glues them to the surface on which the insect walks. 

 When the pads are carefully examined, it will be seen 

 that they have no cup -shaped cavity beneath them, 

 but that they are hollow with a nipple-like pro- 

 tuberance projecting into each. This will be seen 

 more plainly by pressing upon the tarsus which forces 

 it into the pad ; by cutting off the end of the pad 

 first it may be exposed in this manner, and will be 

 found to consist of a closed sac. This sac fills the 

 whole of the last four tarsal joints, and is lined with 

 pavement epithelium; it secretes a perfectly clear viscid 

 fluid, which exudes from it into the pad, and fills its 

 cavity, as well as the hollow hairs with which its under 

 surface is covered. These hairs open by trumpet- 

 shaped mouths, and the disc of each mouth is kept 

 full of the fluid. Sometimes, when the insect is cap- 

 tured and held between the finger and thumb, it 

 exudes so rapidly that the pads are soon covered with 

 a little glistening drop of it, which may be collected 

 upon a glass slide, where it rapidly solidifies. It is 



