PLAY AND INSTINCT. 39 



The same question may be asked about the animals that 

 are hatched out by the sun on the sand, and as soon as 

 they creep out of the egg hurry to the water without 

 being shown the way; of the young duck, too, that in 

 spite of the cries of the clucking hen betakes itself to 

 the strange element. We have incontrovertible proof also 

 that the mechanical impulses are innate and inherited 

 in animals that are taken living from the mother's 

 womb, and so could not by any possibility have seen any 

 others or have learned to act as they do. The cele- 

 brated Swammerdam has made such an experiment with 

 the water snail, which is born alive. He took a little 

 one just ready for birth and placed it in water, where 

 it immediately began to move about quite as well as 

 the mother could. And this implies great skill, for, in 

 order to sink, these snails retire into the shell and com- 

 press the air contained in the end-chambers, thus becom- 

 ing heavier than the water. To rise, they come out a 

 little, causing the inclosed air and their own body to 

 occupy more space and so become lighter than the water. 

 For surface swimming they turn over so that the shell 

 is like a boat, the feet are extended on both sides, and an 

 undulating movement like that of the land snail sends it 

 slowly over the water. This skill and readiness in move- 

 ment the snail cut from its mother's body has certainly 

 not learned nor practised, but brought already developed 

 into the world." I may here point out that Reimarus 

 very rightly emphasizes the difficulty of learning an 

 entirely new kind of movement. If, for example, suck- 

 ing the breast "were not innate skill, so to speak, 

 there is no reason why grown people should not do 

 it as well as children, particularly as they are prac- 

 tised in various movements of the mouth, and even 

 in sucking at other soft tubes. But, speaking for my- 

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