Human Physiology. 



and the shell with its eggs are fastened to a place selected. 

 When the larva is hatched it secretes a fluid which dissolves 

 this cement, and so escapes from its prison. 



Many insects, pursued by enemies, simulate death, as birds 

 pretend to be lame, to lure people from their nests. The dung 

 beetle pretends to be dead but that is not his last dodge. He 

 sticks out his legs and holds them rigid so as to seem more 

 dead, and at the same time make himself an ugly object to 

 swallow. 



Similar to the electric apparatus in the electric eel and torpedo 

 is the insect power of producing light. The glow-worm shines 

 with a steady light, but the fire-fly gives out its light in a strong 

 blaze at short intervals, and I do not know of a prettier sight 

 than a meadow full of fire-flies or lightning-bugs. At intervals 

 of two or three seconds the whole semi-transparent abdomen 

 of the insect is a mass of pale bluish light. If crushed the 

 matter retains its phosphorescence for some minutes. 



The spider is a creature of marvellous structure and powers, 

 spinning webs of great strength and mathematical beauty out 

 of its own body by a complex and admirable apparatus. First 

 it has glands, which, under nervous influence, secrete from its 

 blood, which is formed of its food, a viscid liquid which, the 

 instant it comes to the air, hardens into silk. This liquid, by 

 proper muscles, is pressed through minute orifices in from four 

 to six spinarets, each spinaret in some instances having 4,000 

 orifices, so that 24,000 threads unite, woven together in zigzag 

 lines, to produce one thread one-fiftieth the diameter of a hair. 



The water spider lives in a bell-shaped house under water, 

 lined with soft dry silk, and filled with air which the spider 

 carries down in small bubbles. Others build houses in the 

 ground, beautifully carpeted, and covered with a door which 

 opens with silken hinges. 



The mechanism of fishes for swimming; their propelling 

 tails, so vastly beyond the power of any which have been 



