THE CELL 53 



In the development of any animal it may be stated that, 

 from the outer germ layer, or ectoderm are formed the cover- 

 ing of the body with its protective structures such as scales, 

 feathers and the like, the nervous system and the sense 

 organs. The entoderm or inner germ layer gives rise to the 

 lining of the digestive tube, the gland cells of liver, pan- 

 creas and stomach, the lining of lungs and trachea. From 

 the mesoderm are derived the muscle, bone, connective tissue, 

 blood, heart and bloodvessels, the kidney, reproductive 

 organs and their ducts. 



