THE ECONOMY OF SLEEP 



insects is obscure. Take the earwig. It hibernates 

 freely in the familiar form in which we know it 

 during the summer and early autumn. Only the 

 other day, turning some mossy stones in the coppice, 

 I uncovered an earwig, which was wakeful enough 

 the stones had been warmed perhaps by the sun to 

 run rapidly to shelter. The earwig, perhaps, must 

 feed against the winter fast like other sleepers. 



The deeper the trance the smaller the waste 

 of tissue. Some forms of life fall into trances 

 in order that they may survive moisture famines. 

 One authority stated that certain animalcula had been 

 revived by moisture from a trance of twenty-seven 

 years. It is Humboldt who mentions the alligator 

 and the boa-constrictor of South America as sleepers 

 through seasons of drought. In England snails 

 both hibernate and aestivate. The adder hibernates 

 when its prey hibernates ; what alternative has it but 

 death ? The hedgehog is in the same position. 

 Neither is equipped for migration. But it is interest- 

 ing to turn from these to the English bats and the 

 English birds of summer passage. The bats, except, 

 I think, the pipistrelle, sleep deep through the winter 

 evidently because the moths and other insects on 

 which they feed are also sleeping deeply though 

 not in the winged state, like the brimstone butterfly. 



The birds migrate when the insects on which 

 they feed enter upon winter states egg, chrysalid, 

 or caterpillar. Why do the birds migrate instead 

 of hibernating ? Tremendous dangers attach to 

 migration. Were it not safer for the bird to sleep 

 E 49 



