224 



which we have both the central organ and the lateral flaps. 



The first I have met with has been in the Phri/ganea or case 

 fly, which possesses two well-marked hairy flaps, similar to 

 those of the house fly, and a central palm similar to that of the 

 honey bee. Pig. 29. 



The intention of the two it is difficult to define. The fly has 

 the power of walking for a time upon water, but this does not 

 entirely explain the cause of the complicity of its foot. 



The second I have met with is in a butterfly (name un- 

 known), in which there are the usual hooks and flaps common 

 to the genus, and in addition a central dark pillar, evidently a 

 rudimentary form of the more enlarged organ of the wasp. 

 Fig. 30. 



This account would scarcely be complete without a reference 

 to the fore and middle pair of legs of the male Bytiscus — a 

 large aquatic beetle. 



It is unnecessary to describe both : we will therefore select 

 the former, as more elaborate. In it the upper joints of the 

 tarsus are developed into a circular disc of considerable size. 

 This is furnished with a number of suckers whose construction 

 is very beautiful. The larger ones, rarely exceeding three in 

 number, consist of a circular funnel-shaped membrane, which 

 is capable of being pressed flatly upon any surface, protected 

 externally, by a ring of hairs, and strengthened internally by 

 bands which radiate from the central chimney, and subdividing 

 so frequently as to be almost membraniform at the circum- 

 ference. 



These bands terminate at the top of the funnel, when they 

 are acted upon by muscles. Whenever these are brought into 

 operation they have a tendency to raise the centre of the disc. 

 The smoothness of the circumference prevents the access of 

 fluid, and atmospheric pressure is consequently brought into 

 play. 



In addition to these large suckers, there are others covering 

 the leg in far greater numbers. 



