i;i 1 1:< T or i:\rosrm; ON TIII-: YOUNG 191 



little over one hour. Now exposure ;it th;it 

 teinpeniture is evidently dangerous, hut it, 

 would he still more dangerous if the weather 

 were wet instead of dry, and the temperature 

 Hi F. instead of 50 F. ; and it is, I imagine, 

 on this account that the impulse to brood is 

 s. strongly implanted in the female. No 

 sooner, it seems, does she depart than she 

 returns with a small quantity of food which 

 she hurriedly distributes and immediately settles 

 down to brood ; and if forcibly prevented from 

 returning, her attitude betrays symptoms of 

 what, humanly speaking, we should term great 

 distress. If, then, the conditions in the external 

 environment were such as would make it 

 difficult for the female to obtain food rapidly, 

 what advantage would she derive from so 

 strongly developed an impulse? Might it 

 not be a disadvantage ? Might it not mean 

 that she would abandon the search too readily 

 and be content to return with an insufficient 

 supply, and might not that be as injurious to 

 the young as prolonged exposure ? Manifestly 

 the impulse to brood could only have developed 

 strength in so far as it fitted in with all the 

 other factors that make for survival ; and the 

 principal factor in the external environment 

 seems to be the territory. How could the 

 young have been freed from the risk of 

 exposure if the impulse to brood had not 

 been so strongly implanted in the parent? 

 How could the impulse to brood have been 

 free to develop if a supply of food had not 



