Adaptations to Environment 127 



Another important idea is that littoral haunts, both on the 

 seashore and in the freshwaters, afforded the necessary appren- 

 ticeship and transitional experience for the more strenuous life on 

 dry land. Much that was perfected on land had its beginnings on 

 the shore. Let us inquire, however, what the passage from water 

 to dry land actually implied. This has been briefly discussed in a 

 previous article (on Evolution), but the subject is one of great 

 interest and importance. 



Difficulties and Results of the Transition from Water to Land 



Leaving the water for dry land implied a loss in freedom of 

 movement, for the terrestrial animal is primarily restricted to the 

 surface of the earth. Thus it became essential that movements 

 should be very rapid and very precise, needs with which we may 

 associate the acquisition of fine cross-striped, quickly contracting 

 muscles, and also, in time, their multiplication into very numer- 

 ous separate engines. We exercise fifty-four muscles in the 

 half -second that elapses between raising the heel of our foot in 

 walking and planting it firmly on the ground again. Moreover, 

 the need for rapid precisely controlled movements implied an 

 improved nervous system, for the brain was a movement-con- 

 trolling organ for ages before it did much in the way of thinking. 

 The transition to terra firma also involved a greater compactness 

 of body, so that there should not be too great friction on the 

 surface. An animal like the jellyfish is unthinkable on land, and 

 the elongated bodies of some land animals like centipedes and 

 snakes are specially adapted so that they do not "sprawl." They 

 are exceptions that prove the rule. 



Getting on to dry land meant entering a kingdom where the 

 differences between day and night, between summer and winter 

 are more felt than in the sea. This made it advantageous to have 

 protections against evaporation and loss of heat and other such 

 dangers. Hence a variety of ways in which the surface of the 

 body acquired a thickened skin, or a dead cuticle, or a shell, or a 



