. 2£3 



not for a special system of ribs running the whole length of 

 the flap, of sufficient strength to keep it in its proper shape. 

 These ribs are situated on the dorsal surface of the membrane, 

 and their arrangement differs so much in each of the varieties 

 we have mentioned, that any one of them may be identified by 

 the examination of the foot alone. I have represented three 

 in the accompanying diagrams, Figs. 23, 24, 25. 



In one specimen (Tabanus lovimisj the support assumes the 

 form of double ridges parallel to each other, and going the 

 length of the boss. Fig. 27. 



In another (the Asilns communis) it consists of two strong 

 pillars in each flap, passing in a straight line from the leg to 

 nearly the termination of the hairy flap. Fig. 26. 



In the Tabanus bovinus, in the Zylophagus atety and in the 

 fever fly, the number of bosses is increased by a central one 

 inserted between the two. Fig. 27. 



There is no difference however in the hairy character of their 

 under surface, or in the curve at the end of each individual hair. 



In some insects, the Cymbex lutea, and others, the bosses 

 are situated on the under surface of the four or five last joints 

 of the leg. Fig 28. 



They are, like those on the foot, covered with hairs emi- 

 nently adhesive. 



In one or two instances, I have found them smooth. The 

 motion in these bosses is very limited, and is confined to a 

 pressure downwards, so as to fix them firmly on any plane 

 surface, or to a simple retraction to the leg when they are not 

 in use. 



In the Curculio and others, these bosses are placed in pairs, 

 on each side of the leg, and are comparatively numerous. On 

 some we find the usual adhesive hairs, which in the Curculio 

 are remarkably developed, there being a terminal enlargement 

 at the end of each hair. Kg. 31. On others the hairs are large 

 and coarse, and easily seen by the naked eye. Figs. 13, 14. 



There are one or two specimens occasionally met with in 



