INCUBATION. 
On the first thoughts upon this subject it may appear 
of little importance to the general observer how long it 
may require to hatch an egg, and under what conditions 
it can be hatched, but after a little consideration many 
circumstances will become known that cannot fail to 
impress upon us the powerful and undeviating law that 
exists in all created life, the fixed period for change from 
one state of existence to another, not only observable in 
the advancement of the embryo in the egg, but continuing 
through the whole life of every individual of every species. 
As the most ready and easily-explained examples, let us 
take the eggs of birds : we find an unalterable and 
measured time required for hatching the eggs of one 
class or order of birds, and in this way we find that the 
eggs of some kinds of birds will hatch at a much earlier 
period than others ; as, for instance, the pigeon’s eggs 
hatch at the end of fourteen days, the common fowl at 
twenty-one days, the duck at twenty-eight days, the 
geese at thirty-five. It will be seen by this the remark- 
able regularity of the period of the multiplying of the 
universal seventh day. The longest period required for 
hatching the eggs of birds occurs with the struthious birds 
(ostriches), and the period is seven times seven, or seven 
weeks. It will be thus seen that the earliest time 
recorded will be twice seven and the longest time known 
seven times seven. This certainty of time, as before 
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