THE CIGALB LEAVES ITS BURROW 21 



explains the chamber at the base of the shaft, and the 

 necessity of a cement to hold the walls together, for 

 otherwise the creature's continual comings and goings 

 would result in a landslip. 



A matter less easy of explanation is the complete dis- 

 appearance of the material which originally filled the 

 excavated space. Where are the twelve cubic inches of 

 earth that represent the average volume of the original 

 contents of the shaft? There is not a trace of this 

 material outside, nor inside either. And how, in a soil 

 as dry as a cinder, is the plaster made with which the 

 walls are covered ? 



Larvae which burrow in wood, such as those of 

 Capricornis and Buprestes, will apparently answer our 

 first question. They make their way through the 

 substance of a tree-trunk, boring their galleries by the 

 simple method of eating the material in front of them. 

 Detached by their mandibles, fragment by fragment, the 

 material is digested. It passes from end to end through 

 the body of the pioneer, yields during its passage its 

 meagre nutritive principles, and accumulates behind it, 

 obstructing the passage, by which the larva will never 

 return. The work of extreme division, effected partly 

 by the mandibles and partly by the stomach, makes 

 the digested material more compact than the intact 

 wood, from which it follows that there is always a little 

 free space at the head of the gallery, in which the cater- 

 pillar works and lives ; it is not of any great length, but 

 just suffices for the movements of the prisoner. 



Must not the larva of the Cigale bore its passage in 

 some such fashion ? I do not mean that the results of 

 excavation pass through its body — for earth, even the 



