WATER ESSENTIAL TO ALL LIFE. 223 



the egg comes a larva, and this larva contains much water 

 aud is soft and moist, and possesses nerves and muscles, and 

 many most elaborate organs and tissues, not yet half investi- 

 gated. The larva eats voraciously and gi'ows, but though it 

 is an imperfectly formed inmiature thing for some time, its 

 tissues are most perfect and its movements most delicate and 

 wonderful. Sooner or later, it passes into a state of com- 

 paratively passive living existence as a chrysalis or pupa, 

 which remains, sometimes for many months, as it is said, in 

 a " dormant " state, within its dry outer envelope. But 

 the living growing substance of the chrysalis is vavy moist 

 and in many instances quickly undergoes the most wonderful 

 vital changes. 



Almost the whole of the inside of the chrysalis consists of 

 moist living inatter. The tissues which are gradually being 

 formed are totally different in every respect from those of 

 the larva, grub or caterpillar. These tissues become very 

 distinct as the time for the great and final cliange approaches ; 

 Avhen at last what is in fact a new creature with organs, 

 structures, and powers different in nature, and even in the 

 principle of living action, is evolved, aud sees the light. In 

 short, after wonderful constructive changes have been 

 going on for some time, the various structures of which the 

 imago, or final stages of the butterfly or beetle, or other 

 insect, appear in perfection. The air tubes by which the 

 insect breathes, the muscles, nerves and the more complex 

 organs and structures of the imago are all developed 

 in the chrysahs stage. An insect has no lungs, the air 

 is conveyed to the ultimate parts of the different tissues 

 •direct, by little tubes or tracheas, wdiich open on the 

 external surface of the insect. The air is drawn in and 

 passes through these tubes, which extend to every part of 

 the tissues and organs, by the movements of the body, and thus 

 the fluids and tissues in all parts of the organism are supplied 

 with air. The air is in fact taken direct to the tissues. 

 In the act of breathing in the vertebrate animal and man, 

 on the other hand the air is taken up by the blood as it 

 traverses the blood vessels of the lungs, and after passing 

 to the heart, the aerated blood is distributed to all parts and 

 tissues by means of the systemic vessels. The air is dissolved 

 by the blood, and the oxygenated fluid filters through the 

 thin walls of the capillaries, and thus reaches all the different 

 organs and tissues of the body. 



Every part of the active living matter is moist and 



