215 



modified in the same way as those of the Anthoinyia. The 

 only difference being in the number of the divisions of the 

 toes, so to speak. 



We now come to the simplest form of the most extensive 

 genus met with in the insect world — the double hook. 



In this variety, the foot consists of two simple hooks of 

 great hardness, which are articulated to the last joint of the 

 tarsus by a simple joint. Figs. 13, 14, IG. This, as far as I 

 have been able to discover, is of the ball and socket kind, so 

 as to give a power of motion in every direction. Fig, 16. 



The motion is regulated by powerful muscles, which may 

 be shown in recent specimens by tearing them from their 

 attachments in the forcible removal of the claw. 



They cannot be shown well when the foot is preserved in 

 Canada Balsam as a microscopic preparation. 



It would be difficult to say whether the claws are more 

 commonly used as claspers with each other, or whether they 

 are used as hooks principally, and only form claspers when 

 brought dow^n upon the tarsus. 



Examples of both occur, and may be readily noticed with 

 the naked eye in the large beetles, dragon flies, etc. The use 

 of them as hooks seems perhaps the most constant. There is, 

 however, an interesting exception. 



Many of you will be doubtless familiar with the Ilydrometra 

 stagnorum, an elegant little fly, which may be seen sporting in 

 great numbers upon the surface of still water during warm 

 and sunny weather. 



These move about with great velocity, and if they are closely 

 examined, they will be found to be resting upon the under 

 surface of the greater part of the leg, and not upoft the last 

 joint of the tarsus only. 



The integument is covered with an immense number of fine 

 hairs, to which the atmospheric air strongly adheres ; they are 

 probably also coated with a secretion not readily miscible with 

 water. Fig. 38. 



