176 NATURE STUDY 



fine scissors or sharp scalpel or knife cut open the skin along the 

 median line of the back from end to end of the body. Spread the 

 skin out on each side of the body and pin the cut edges down. 

 Then pour into the dish enough clear water to cover the specimen, 

 and with needles and forceps pull apart the white masses of fat 

 until the conspicuous dark longitudinal tracheal trunks are 

 exposed. The air tubes will appear either dark or shining 

 silvery. All air tubes (tracheae) are finely transversely lined or 

 striated. These fine transverse striae are really a continuous 

 elastic thread which runs spirally around on the inner surface of 

 the air tube and which by its elasticity, holds the tube open. A 

 bit of one of these large air tubes cut out, and mounted in a drop 

 of water or glycerine on a glass slide, should be examined with a 

 magnifier, so as to see this characteristic transversely striated 

 appearance. 



In the case of other animals, not insects^ the air which i& 

 breathed in is carried by short tubes to an organ (the lungs) 

 where it meets the blood and gives up its oxygen to it. The 

 blood then carries thru the blood tubes (arteries) this oxygen to 

 all parts of the body. But with insects, as we have seen, the air 

 is carried in tubes of its own all over the body. This is 

 one of the most important physiological peculiarities of insects. 



All insects which live in the air, i. e., which do not live in 

 water, breathe as the locust does. That is, they breathe thru 

 small holes which are situated in a single row on each side of 

 the body. But many insects live in water. How do they 

 breathe ? 



An account of the manner of breathing of several water 

 insects is given in the chapter "Some Water Insects." 



