LECTURE IV 



SOME OF THE MODIFICATIONS OF THE REPRODUC- 

 TIVE PROCESS AS ADAPTATIONS TO LIFE 

 UPON LAND 



As was the case with the Vegetable Kingdom, all the 

 evidence goes to show that animals were originally 

 inhabitants of the water. However, as Evolution has 

 proceeded, many different groups of animals have taken 

 to the land, being enabled to survive there by various 

 interesting modifications. The most conspicuous of these 

 is the development all over the surface of the body of 

 an impermeable layer to prevent the drying up of its 

 substance for living protoplasm has been unable to 

 accustom itself to drying up. It may probably be said 

 truly that " Dry protoplasm is dead protoplasm." The 

 impervious outer coating of the land animal fulfils then 

 an important function in retaining the moisture within 

 the body. 



Enclosed within this covering is the cell community 

 these myriads of highly specialized and actively co- 

 operating cells that constitute the living body. Each of 

 these has its surface in contact with the watery fluid 

 which everywhere permeates the body. The individual 

 cells lives in this fluid just as a simple protozoan animal 

 lives in its pool or pond ; and Nature has adapted the 



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