184 



LIFE: ITS NATURE AND ORIGIN 



grams showing in part what is seen when a zygote develops into 

 an individual. "Everyone has been impressed by the miraculous 

 transformation of the sticky white and yellow mass of hen's egg 

 into a fully dressed, befeathered, respectable chick, all in 21 days. 



ALLANTOIS 



AMNION 



/ 



ALBUMEN — — YOLK SAC 



5 DAYS 



ALLANTOIS 



AMNION 



ALBUMEN YOLK SAC 



10 DAYS 



BLASTODERM 

 I 



AIR-CELL 



SHELL MEMBRANE 



Figure 29. Domestic fowl's egg and its development. Beginning of alimentary 

 tract, 18 hours; vertebral column, 20 hours; nervous system, 21 hours; head, 22 hours; 

 blood island-vitellin circulation, 23 hours; eye, 24 hours; ear, 25 hours; heart beat, 

 42 hours; amnion, 50 hours; legs and wings, 63 hours; allantois, 70 hours; reproduc- 

 tive organs, 5th day; feathers, 8th day; beak turns toward air cells, 17th day; yolk sac 

 begins to enter body cavity, 19th day; yolk sac completely drawn into body cavity, 

 20th day; hatching of chick, 21st day. (Courtesy A. L. Romanoff, Cornell Exp. Bull. 

 205, 1931 and 1936). (From Brody's "Bioenergetics and Growth.") 



The original egg cell must have travelled at a dizzy pace to build 

 up so complex a mechanism — probably exceeding in complexity* 

 the astronomical wonders with their galaxies and supergalaxies." 4 

 The following epitome of the development of a mammalian egg 

 is more detailed. 



* This, of course, applies to structure levels where stars may be considered as units. 

 On this relatively tiny satellite (the earth) of a medium size star (the sun), untold 

 numbers of similar miraculous transformations proceed daily. J. A. 



