THE WAYS OF LIFE 229 



from being a mere luxury) an instinct is always service- 

 able. 



That animals are sometimes led astray by ' following 

 their instincts ', is well known ; the birds who act as a 

 cuckoo's foster-parents illustrate this. That the hereditary 

 endowment is often insufficient for every emergency, is 

 also well known ; thus cattle will sometimes eat poisonous 

 herbs. But there is no difficulty here, since, on the whole, 

 creatures are well served by their instincts. It is impos- 

 sible that all instincts should be perfect in animals whose 

 environment is changeful or who change their environment. 



The Norwegian lemmings, when they form migratory 

 bands, often head westwards, and continue on their way 

 with great persistence and considerable pugnacity. They 

 swim across lakes, but are apt to lose their bearings in the 

 water and drown. As they march, their ranks are thinned 

 by birds of prey and small carnivores ; even the reindeer 

 trample them underfoot. It is often but a small percentage 

 that reach the shores of the North Sea a select band of 

 survivors deserving a better fate. For, true to their instinct 

 to go on, they swim into the sea and are drowned. In a 

 case vouched for by Collett, a vessel sailed for fifteen 

 minutes through a swarm, the water being alive with 

 them as far as the eye could reach. What must be noted 

 in a case like this, is, that the go-ahead instinct is often 

 serviceable, though it cannot avail against a famine or the 

 occurrence of seas on the earth's surface. 



The instinct to go on is very strong in eels, and its general 

 effectiveness is manifest. It carries them over difficulties 

 and unfavourable conditions if these are not too long 

 drawn out. It can hardly be urged as an imperfection that 

 these persistent creatures, both as elvers and afterwards, 



