THE MARVEL OF GROWTH 



III 



wing is showing itself somewhat, and the ends of the leg, 

 we can see, will by expansion form the foot." 



After ten full days of growing we have a chick with 

 feathers beginning to grow over the entire body. Within 

 those ten days the two germ cells which joined to form the 

 beginnings of the chick have multiplied themselves into this 



ELEVEN STEPS IN THE EARLY GROWTH OF AN EMBRYO 



From a photograph of a set of models, showing each cell enormously magnified. 

 The last three models show longitudinal sections and indicate how the layers are 



being formed 



astonishing result. Never again in later life does any chick 

 increase in size with such surprising speed as is shown by 

 the growing embryo of this oviparous l animal. 



The special point to bear in mind is that, from start to 

 finish, this whole process of growing is nothing more nor 

 less than the dividing and the subdividing of the two germ 

 cells which were joined as one. This first combination cell 



1 Animals developed from an egg are called oviparous. 



