134 OUR HOUSEHOLD INSECTS 



and the tarsus is the only part that is applied to the 

 ground, the tibia and femur being set at an angle to the 

 tarsus and to one another. Now it is obvious that when 

 the front leg is advanced and placed in position for a 

 step, it is in a state of extension, the thigh being set at 

 an obtuse angle to the shank ; but the hind leg, under 

 the same circumstances, is in a state of contraction, the 

 thigh and shank being drawn more closely together. 

 Therefore, when the body is advanced, the front leg is 

 bent up , and the hind leg opened out ; in other words, 

 the front leg acts in such a way as to pull the body 

 along, the claws at the end of the feet giving secure foot- 

 hold meanwhile. The hind leg, on the other hand, is not 

 a pulling but a pushing organ, while the middle leg of 

 the opposite side serves chiefly as a support and pivot 

 for the body. The whole of these movements are effected 

 by means of muscles inside the legs, each of which has 

 one end of itself attached to one division of the leg, and 

 the other to the succeeding one. Such, then, is the 

 method of locomotion of the cockroach, and not only of 

 it, but of every creeping, walking, or running six-footed 

 animal. Most swimming and jumping insects, naturally 

 enough, however, adopt a different style, the correspond- 

 ing legs of the opposite sides being moved simultaneously 

 instead of alternately. 



The digestive system of the cockroach (Fig. 40) is 

 very complete, and as there is not much difficulty in its 

 dissection, any one may easily make out its details for 

 himself. The only thing to be borne in mind is that all 

 such delicate dissections as these should be performed 

 under water, i.e., the insect is fastened to a layer of solid 

 paraffin or cork (or any other substance that will receive 

 and hold pins readily), with which the bottom of a shallow 

 dish has been coated, and then water has been poured 



