THE FLY. 51 



in a former letter; whilst those in the halter es and 

 wings project from the surface (PI. VI. fig. 3, a and h), 

 nerves having been traced to both sets of organs. 



The last, but by no means the least interesting of 

 the Fly's members, to which we shall draw your atten- 

 tion, is its leg, and more especially the final or 

 "tarsal" joint. The leg of the Fly (and indeed of 

 insects in general) is divided into five distinct limbs 

 or joints : the first of these is the " coxa," or hip, by 

 which the leg articulates upon the body (PI. VI. 

 fig. 4, a) ; then the " trochanter," a short round 

 joint (PI. VI. fig. 4, h) ; next the "femur," or thigh, 

 the largest of the five joints (4, c) ; the " tibia," a 

 somewhat thinner member (4, d) ; and lastly, the 

 " tarsus," or foot (4,/) . None of these are distin- 

 guished by any feature of peculiar interest, excepting 

 the last-named ; but that one we shall find quite de- 

 serving of a closer examination. 



The " tarsus" or foot of the Fly is subdivided into 

 five joints, the final one being furnished with that 

 remarkable apparatus which enables the insect to 

 vralk upon what appear to us perfectly smooth or 

 polished surfaces, and also to progress in a position 

 opposed to the laws of gravity. 



This apparatus consists of two moveable claws 

 (PI. VII. fig. 1), resembling a cow's horns in shape, 

 which the insect can affix to any little eminences or 

 depressions that present themselves in its course ; and 

 further, of a pair of membranous expansions, termed 

 " pulviUi," or, familiarly, pads, which, when magnified 



d3 



