396 nature's teachings. 



quite sufficient ; but when the progress of civilisation requires 

 that the eggs of poultry should be hatched in numbers too 

 great for the powers of the parent bird, Man has been fain to 

 imitate Nature, and to invent machines whereby eggs can be 

 hatched by artificial heat, regulated to the temperature of the 

 hen's body. 



Yarious as are these machines in detail, they are all alike in 

 principle, and the right-hand figure of the accompanying illus- 

 tration will give a fair idea of the method which is employed. 



A box is fitted up with trays, on which the eggs are 

 arranged. At the bottom of the box there is the heat- 

 producing apparatus, which can be regulated at pleasure. The 

 trays of eggs can be moved from one part of the box to 

 another, so as to insure the right amount of heat, and, if this 

 process be only carefully carried out, the young chicks emerge 

 from the eggs exactly as they would have done if the hen had 

 sat upon them. 



This machine is sometimes called the Artificial Mother, and 

 it is worthy of notice that it is no modern invention, the ancient 

 Egyptians having used it more than three thousand years ago. 



With regard to Nature, it would have been simple enough 

 to give one illustration of a bird sitting on her eggs, but I 

 have preferred to select a different subject, as more relevant to 

 the question of artificial heat. 



There is an insect to which we have had several occasions of 

 reference, namely, the Wurble-fly of the ox, scientifically 

 known as CEstrus bovis. 



The eggs of this insect are deposited in the skin of the ox, 

 and are there hatched by the heat of the animal. In propor- 

 tion as the larva grows, it raises lumps upon the skin, these 

 being practically the roofs of the artificial home. There are 

 several other species of the same genus, all of which have their 

 eggs hatched by the heat of the animals on which they are 

 placed. There are, for example, the common Bot-fly [CEstrus 

 equi), whose eggs are hatched in the interior of the horse, 

 and the Sheep-fly (CEstrus ovis), whose eggs are hatched in the 

 head of the sheep. The common Snake leaves her eggs to be 

 hatched in the artificial heat produced by decaying vegetable 

 matter. 



