CAUSE OP HEREDITY 265 



earth, grass and brush. A little later on the railroad came 

 through the country and brought lumber for better 

 houses. This simply goes to show that man adapts him- 

 self to conditions, just as other animals do. 



However, what I started to show was this, that the 

 rat knows how to build houses over the water in which 

 to live, and not houses in the trees like squirrels, nor 

 houses in the ground like the badger. The building of 

 the houses of the muskrats is an experience and ability 

 possessed by this animal alone, that is, by the cells in 

 his brain. They know how to build these and none other. 

 The houses of the muskrat are always about the same. 

 They are for a specific purpose. They are intended to 

 provide the occupants with a place to live over the water 

 in the severe winter, with entrances into the water under 

 the ice, where they can obtain the roots, insects and grass 

 in the water for food. They must be just so, or they 

 would not answer the purpose. It requires considerable 

 skill to build these houses because the thick ice, which 

 will cover the marsh in the coming severe winter, must 

 be correctly calculated. The singular thing about this 

 animal, as well as other animals and birds, is that it knows 

 how to build these houses without ever having seen one 

 before, and without ever having had any previous instruc- 

 tion in the art. He is born with the knowledge. We shall 

 see upon further investigation that this knowledge is lo- 

 cated in certain cells of the body. The cells that build 

 the rat not only know how to build him as a structure 

 specifically adapted to live in water, but also know how 

 to build another structure for his home, using him as a 

 machine with which to do it. The young duck knows that 

 it is proper to jump into the water, and goes in the first 

 opportunity it gets, while a young chicken will keep away 

 from the water. Without having had any previous ex- 



