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This system of giving birth is called viviperous, in contra- 

 distinction to the oviparous, as, where eggs are laid by most 

 insects and all birds, and the young are brought forth by 

 the application of heat, either naturally, as when the bird 

 sits upon the egg, or the natural temperature of the air 

 brings out the young larvae, or artificially, as when heat is 

 applied ; therefore on the application of a certain amount 

 of heat the vital principle, until now dormant, is called into 

 active existence. To watch the progress day by day of the 

 development of life is of intense interest, and the following 

 simple arrangement is all that is necessary. 



Take a tin square box eighteen inches over and eight 

 inches deep, fill it half full of sand ; have a ledge outside 

 that it may drop only four inches into another box contain- 

 ing water; this may stand upon four legs— on keeping an 

 oil lamp uuder it with a screw to raise and lower (he wick, 

 and with a thermometer in the bath to regulate the heat, 

 which should for twenty-one days never fall in the twenty- 

 four hours below 96° Fahrenheit. You will find that the 

 eggs (if vitalized) will be opening and the little chicks 

 coming out. Now from their size it would be very difficult 

 to observe the changes going on in the eggs of moths ex- 

 cept under the microscope ; but if a sufficient supply of 

 birds' eggs were placed in the tin box by taking one out 

 every six hours and breaking it, the whole system becomes 

 revealed, and from the simple fertilized cell through all the 

 marvellous developments of parts, until the little chicken, 

 with its primitive clothing, a type of its parent, comes forth, 

 we can trace the organic progress. The feathers no doubt 

 differ in colour to the adult plumage, but here we have 

 similarity of form, and an internal organization for all 

 practical purposes of strong resemblance. But if by the aid 

 of the microscope we watch the advancing germ in the egg 

 of a moth, instead of finding, as progressive growth brought 

 the little creature nearer to its period of liberation, it took 

 on the form of a winged and perfect insect, we should see a 

 little worm-like body, and if we watched its exit we should 

 find it biting its way out by enlarging the aperture it had 



