217 



The surface at the summit often appears to be imbricated or 

 covered with scales, indicating its formation originally by cells. 



We have now reached, by gradual ascent, our second class 

 of feet, which we shall describe under two heads : those with 

 one central hairy membraniform disc, or other appurtenances, 

 and those having more than one, attached either to the foot 

 or to the joints of the tarsus. 



It is I think highly probable that there are no double hooks 

 without a central disc ; but as this is certainly rudimentary in 

 those we have described before, I prefer beginning with those 

 in whom it is largely and decidedly developed. 



We will notice first a fly called Ophion. In its foot we 

 find two large and beautiful hooks armed with deep serratures 

 like the claws of the spider ; between them is a strong pillar 

 to which the hooks are laterally attached. This carries at 

 its free extremity a soft cushion, covered over with nu- 

 merous hairs, and a naked membrane perfectly clear and 

 transparent. These are usually found covered with pollen or 

 dust and the foot requires to be well cleansed before it can be 

 thoroughly examined. Tig. 6. 



The deep serratures of the claws, and their close resemblance 

 to those of the spider, will at once suggest the idea that they 

 must have a common use. 



In the Panorpa communis a similar appearance is found. 

 These insects spin webs, and the foot is evidently modified 

 to enable them to walk with ease over and about them. 



In the last named species the central organ of the foot re- 

 ceives a very remarkable development. It resembles most 

 closely an inverted cone, slightly flattened from side to side, 

 and divided on the upper flat surface. A broad double headed 

 bar strengthens it at this part, and prevents the cone from 

 opening too far. The interior seems to be hollow, and fur- 

 nished as is the exterior, with many minute hairs. Fig. 15. 

 It is evident that considerable use is made of the cone, as 

 there is a special process adapted for its insertion. 



2 F 



