io6 



FEET 



CHAP. 



when extended it is seen that the pressure plate is bent twice at 

 a right angle so as to form a step, the distal part of which runs 

 along the upper face of the basal part of the pad ; the apical 

 portion of this latter consists of two large lobes, which in repose, as 

 shown in our Figure (/), fall back on the pad, something in the 

 fashion of the retracted claws of the cat, and conceal the pres- 

 sure-plate. 



The mode in which Insects are able to walk on smooth 

 perpendicular surfaces has been much discussed, and it appears 

 highly probable that the method by which this is accomplished 

 is the exudation of moisture from the foot ; there is still, how- 

 ever, much to be ascertained before the process can be satisfactorily 



Fig. 59. Foot of Pelopaeus, a 

 fossorial wasj^ : A, tarsus entire ; 



B, terminal joint, upper side ; 



C, under side. a, claw ; &, 

 base of pressure-plate ; c, ex- 

 tension - plate ; d, extension- 

 sole ; e, pad ; /, lobe of pad 

 retracted. 



comprehended. The theory to the effect that the method is the 

 pressure of the atmosphere acting on the foot when the sole is 

 in perfect apposition with the object w^alked on, or when a 

 slight vacuum is created between the two, has apparently' less to 

 support it. 



The legs of the young Insect are usually more simple than 

 those of the adult, and in caterpillars they are short appendages, 

 and only imperfectly jointed. If a young larva, with feet, of 

 a beetle, such as Crioceris asparagi be examined, it may be seen 

 that the leg is formed by protuberance of the integument, 

 which becomes divided into parts by simple creases ; an observa- 

 tion suggesting that the more highly developed jointed leg is 

 formed in a similar manner. This appears to be really the case, 



