THE WINGS AND LEGS. 19 



for, by taking a recently killed fly and using a pair of dissecting 

 forceps, placing one blade behind, and the other in front of the 

 upper part of the thorax, the movements of flight may be pro- 

 duced by'alternately compressing and relaxing the forceps ; the 

 wings should be extended in order that the full effect may be 

 seen. The amount of alteration in the convexity of the back 

 which is sufficient to depress the wings to their fullest extent, is 

 so slight that it is scarcely perceptible to the eye. 



It is a remarkable fact, and one worthy of special attention, that 

 the great longitudinal thoracic muscles exhibit no striae, but con- 

 sist of muscular fibres similar to those of organic life in the higher 

 animals. This is an anomaly for which I can suggest no reason, 

 unless it be the immense rapidity of the vibrations into which 

 they throw the thoracic parietes.* 



The legs consist of four parts : the coxa or hip, composed of two 

 pieces, which unites the limb to the thorax, the femur or thigh, the 

 tibia or leg, and the tarsus or foot ; the last three are tubular, and 

 each articulation contains the muscles which move the succeeding 

 one. The tarsus consists of five pieces, the first of which contains a 

 pair of muscles, which move the second upon it, but the remaining 

 four contain none ; the last bears a pair of pads upon which 

 the insect walks, and a pair of hooks above them. Both hooks and 

 pads are connected with a single apodeme which projects into 

 the last tarsal joint and is continued as a fine chitinous thread 

 or tendon through the tarsus and tibia, and terminates in a bi. 

 penniform muscle which arises from the interior of the 

 femur. 



The foot pads are amongst the most interesting parts of the insect, 

 because they enable it to walk upon smooth surfaces in an inverted 

 position, apparently in defiance of the laws of gravity. Long ago 



* The description of the histological elements of these muscles is given 

 at page 5. 



C 2 



