INJURIOUS INSECTS OF 1904. 161 



pushes earth before him, it presses on the cork or potato, fires the 

 gun and never fails to kill the animal in the burrow. A trap said 

 to be excellent, of comparatively recent invention, is shown in 

 Figs. 150 and 151. This is placed in the gopher's burrow, and is 

 kept set by a string, as shown in Fig. 150. The animal seeing this 

 string, and realizing that it is foreign to his dwelling, proceeds 

 to gnaw it. The result of his biting the string is shown in Fig. 

 152. The trap sells for 35 cents, three for $1.00, and is manu- 

 factured in Chicago. 



Fig. 152. — Pocket Gopher caught in Trap. 



The prominent front or incisor teeth or rodents, upon which so 

 much depends in the way of subsistence, are peculiar in that while 

 the front of each tooth is hard enamel, back of this is compara- 

 tively soft dentine, the enamel in front being much thicker than 

 anywhere else on the tooth, and the chisel-like sharpness of these 

 teeth is brought about and maintained in each case by working 

 against the opposing tooth in the opposite jaw. As we can readily 

 see, the working of the enamel edge in the lower teeth against the 

 inner or dentine surface of the upper teeth, and vice versa, would 

 result in a sharp enamel edge in both upper and lower teeth. If, 

 as sometimes happens, through disease or by accident one incisor 

 is lost, or both, the opposing tooth or teeth in the upper or lower 

 jaw, as the case may be, keeps growing, not being worn away at 

 the free end, as would be the case normally, and completes an arc 



