The digestive canal represents a tube passing through the entire organism and communicating with the external world, i.e. as it were the external surface of ...

The digestive canal represents a tube passing through the entire organism and communicating with the external world, i.e. as it were the external surface of the body, but turned inwards and thus hidden in the organism.

quote by Ivan Pavlov
Submitted by Lucian Velea
Vote! | Copy!