THE PATH OF EVOLUTION 



bird. In the egg above named, on careful examina- 

 tion, there will be found, always on the upper surface 

 of the yolk, a white, circular, disk-like spot; the 

 Cicatricula, about one-quarter of an inch in diameter 

 (.006 m), that is uncovered by the layer of vitelline 

 or gelatinous albumen the " white of the egg " that 

 surrounds it. A sort of canal, formed of the gelatinous 

 vitelline, connects it with the centre of the yolk, in 

 which there is a cavity. In the middle of the little 

 disk is a small, membranous, somewhat lenticular, 

 white body, from one-sixteenth to one-twelfth of an 

 inch in diameter (.001 5 to .002 m) ; it is transparent, 

 and the surrounding margins have a radii-like struc- 

 ture. This is the fertilized germi native vesicle. In 

 it alone is the potency of the future life. All the 

 rest of the egg is to serve only for its protection and 

 nourishment. At the centre of the larger end of the 

 egg a small vacuous space is formed by the vitelline 

 detaching itself from the shell and investing mem- 

 brane. This space, which increases from day to day, 

 is filled with air that enters through the pores of the 

 shell. If kept in a cool place, at a temperature of, 

 say, 40 to 60 degrees F., an egg will retain its proper- 

 ties for a number of days ; it will also resist a low 

 temperature. It has retained its vitality even when 

 exposed to the cold of 10 degrees F. A fresh-laid 

 egg has a specific gravity of 1,078 to 1,094. It 



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