THE NERVOUS SYSTEM 



with marvelous precision ; and the subterranean cham- 

 bers of ants and the dikes of the beaver show engineer- 

 ing skill ; while salmon go from the ocean up the rivers 

 to spawn ; and birds of the temperate zones migrate 

 with great regularity. 



But in the midst of this automatism there are the 

 glimmerings of intelligence and free will. We see some 

 evidence of choice and of designed adaptation. Pure 

 instinct should be infallible. Yet we notice mistakes 

 that remind us of mental aberrations. Bees are not so 

 economical as has been generally supposed. A mathe- 

 matician can make five cells with less wax than the bee 

 uses for four; while the bumblebee uses three times 

 as much material as the hive bee. An exact hexagonal 

 cell does not exist in nature. Flies lay eggs on the car- 

 rion plant because it happens to have the odor of putrid 

 meat. The domesticated beaver will build a dam across 

 its apartment. Birds frequently make mistakes in the 

 construction and location of their nests. In fact, the 

 process of cheating animals relies on the imperfection 

 of instinct. Nor are the actions of the brute creation 

 always perfectly uniform; and, so far as animals con- 

 form to circumstances, they act from intelligence, not 

 instinct. There is proof that some animals profit by 

 experience. Birds do learn to make their nests ; and 

 the older ones build the best. Trappers know well that 

 young animals are more easily caught than old ones. 

 Birds brought up from the egg, in cages, do not make 

 the characteristic nests of their species ; nor do they 

 have the same song peculiar to their species, if they 

 have not heard it. Chimney swallows certainly built 

 their nests differently in America three hundred years 

 ago. A bee can make cells of another shape, for it some- 

 times does ; its actions, therefore, being elective and con- 

 ditional, are in a measure the result of calculation. 



