3;i8 



ZOOLOGY. 



cuneiform, staff-like bodies, with very finely-pointed ex- 

 tremities (primitive nerve-fibres ?), which are surrounded 

 by loosely aggregated ganglionic globules." (Siebold's 

 Anatomy of the Invertebrates.) 



In walking, the locust, beetle, or, in fact, any insect, 

 raises and puts down its six legs alternately, as may be 



seen by observing the movements 

 of a beetle (Fig. 287). While the 

 structure of the limb of a ver- 

 tebrate and insect is not homol- 

 ogous, yet the mechanism or 

 functions of the parts are in 

 the main the same, as indicated 

 in Pigs. 288 and 289. 



The footprints of insects are 

 sometimes left in fine wet sand 

 on the banks of streams or by 

 the seaside. 



In Fig. 290 the black dots 

 are made by the fore, the clear 

 circle by the middle, and the 

 black dashes by the hind legs 

 (Graber). 



The wings are developed as 

 folds of the integument, and 

 strengthened by hollow rods 

 called "veins ;" their branches 

 called "venures." There are 

 in the wings of most insects 

 six main veins — i.e., the costal, 

 the subcostal, median, subme- 

 dian, internal, and anal. They 

 hollow and usually contain an air-tube, and a nerve 

 often accompanies the trachea in the principal veins. The 

 arterial blood from the heart (as seen in the cockroach by 

 Moseley) flows directly into the costal, subcostal, median, 

 and submedian veins ; here it is in part aerated, and returns 

 to the heart from the hinder edge of the wings through the 

 hinder smaller branches and the main trunks of the internal 



Pig. 388.— Section of the fore leg' of 

 a Stag beetle, showing the muscles. S. 

 extensor, i?, flexor of the leg ; a, ex- 

 tensor ; b, flexor of the femur; o, femur; 

 u, tibia;/. taiBus ; A, claw, 109i, s, 

 extensor," 6, flexor of the femoro-tibial 

 joint, both enlarged. — After Graber. 



are 



