358 NATURE'S TEACHINGS. 



with blood-vessels, and therefore the air, instead of being 

 restricted to the lungs, is conveyed to every part of the insect, 

 the air-vessels extending to the very tips of the wings and 

 antennae, and to the claws of the feet. 



Neither does the insect receive the air through mouth or 

 nostrils as we do. Along the sides of the body are certain oval 

 apertures called " spiracles," from the Latin word spiro, which 

 signifies breathing. These spiracles can easily be seen by 

 examining an ordinary silkworm. They are situated in the 

 soft and flexible skin which connects the rings or segments of 

 which all insects are composed, and pass directly into two 

 large air-tubes which run on either side of the body. 



It is evident that since an insect is so thoroughly permeated 

 with air, it must be furnished with means to render that air as 

 pure as possible, and at all events to preserve the respiratory 

 system from being choked with dust or other adventitious sub- 

 stances. 



How important the air is to an insect can easily be seen by 

 dipping it in oil, or even brushing an oiled feather on its sides 

 so as to fill up the spiracles. A man under the hands of the 

 hangman or garotter could not die more swiftly, so much does 

 an insect depend on air. In fact, an insect is almost wholly 

 composed of air-tubes, but for which the great thick-bodied 

 dor-beetles could never use their organs of flight. 



Of course, although the spiracles can act as filters as far as 

 the air is concerned, they cannot be analysts, and consequently 

 insects are peculiarly obnoxious to a bad atmosphere. There is, 

 for example, the well-known "laurel-bottle" of entomologists. 

 A few young laurel-leaves are crushed and placed in a bottle. 

 As soon as an insect is introduced, it breathes the prussic acid 

 which is exhaled from the leaves, and at once dies. 



So it is with the more delicate " death-bottle," into which a 

 little cyanide of potassium is introduced, and covered with 

 plaster of Paris. The plaster prevents the poison from touching 

 the insects and damaging their beautiful colours. It permits 

 the deadly vapour to roll through its interstices ; consequently, 

 even the large-bodied moths, which are tenacious of life almost 

 beyond credibility, .can barely run round the bottle, when 

 they roll over, and expire almost without a struggle, the 

 venomous atmosphere having saturated the entire body. 



