CHAPTER IV. 

 THE INCUBATION OF HENS' EGGS. 



The Egg and its Structure. — T]ie analog}' hetwefii tlie egg 

 and the grains is in many ways closer than between the 

 egg and any animal product commonly found on farms. 

 Each rejjresents an analogous stage in the reproductive 

 cycle. Each contains, besides the living part, which develops 

 into a new organism, enough food material to nourish that 

 organism imtil it can seek nourishment for itself. Witli such 

 grains as corn and wheat, where the food material is stored 

 in an endosperm which is merely connected with the embryo, 

 rather than in cotyledons which are a part of it, the analogy 

 may be i>ressed still closer, because the food material in the 

 egg is merely comiected with the living ])art. 



There are, however, certain interesting differences. The 

 food material stored in the grain consists of starch, oil, and 

 protein, wliile that of the eggs is fat and protein. The 

 grain does not contain enough moisture for development, 

 and must increase its moisture content about 201) per cent 

 before it can germinate. The egg contains sufficient moisture 

 for its own development, and though it is sometimes necessary 

 to retard the evaporation of egg moisture, the egg does not, 

 so far as is known, ever increase its moisture from outside 

 sources. Grains germinate over a range of temperature 

 running from nearly freezing, in the case of wheat, to about 

 103° F. While eggs will start to develop at a much lower 

 temperature than is popularly supposed (08° F.), the range 

 for eggs is not nearly so great as it is for seeds. The optimum 

 germinating temperature for most seeds is around 80° I'\, 

 while the optimum incubating temperature is close to 103° 

 F., with an upward limit whicli Kellicott' states is 41° C. 

 (105.8° F.). 



^ Chordate De\'clopnient. 



(175) 



