290 



REPRODUCTION OF ANIMALS 



2 days 



5 days 



10 days 



15 days 



20 days 



As development of the egg takes place, more and 

 more differentiation occurs. The yolk serves as the 

 food for the developing organism. First the cir- 

 culating system may be recognized, later the head, 

 limbs, and other organs. When the animal is com- 

 pletely developed, it pecks its way out of its shell. 



