80 THE COCKROACH [CH. Ill 



in the air, and that it is by this substance that they retain 

 their hold. The feet do not act as sucking discs, like the 

 familiar india-rubber contrivance for fastening a candle to 

 the window of a railway carriage, for it has been shown 

 by experiment that their adhesive power is in no way 

 impaired by the removal of atmospheric pressure. 



When a cockroach runs (it seldom walks) the legs are 

 moved in a definite order, and the functions of the three 

 pairs differ. The middle leg of one side is moved forward 

 at the same moment as the anterior and posterior legs of 

 the other, this constituting one step. Three legs at least 

 are therefore always in contact with the ground, the tarsus 

 being the part that bears the weight : the animal adopting 

 a "three-point system" of support is in fact a tripod, 

 when running. The legs are so placed that the front leg 

 is extended when it advances, but the hind leg on the 

 contrary is contracted, to bring about movement in the 

 same direction, the femur and tibia of the latter being 

 brought close together. Accordingly, when the whole body 

 is moved forward by these limbs, the front leg pulls and 

 becomes bent up while the hind leg pushes and becomes 

 extended (this last feature is seen in an exaggerated con- 

 dition in the nearly allied relatives of the cockroach, the 

 grasshoppers and locusts). The middle leg of the other 

 side serves mainly as a support for the body. 



Food and digestion. Cockroaches will eat almost 

 anything all that is food for man, whether of an animal 

 or vegetable kind, paper, leather, refuse of every kind and 

 description, and even the dead bodies of their fellows. 

 They are also said to devour bed-bugs and are requested 



