i8o THE EVOLUT10XIST AT LARGE. 



existence. On the other hand, the possession 

 of an operculum, unimportant as it may be to 

 the life of the animal, is a good test of rela- 

 tionship by descent. All snails which take 

 to living on land, whatever their original 

 form, will acquire lungs : but an operculated 

 snail will retain its operculum, and so bear 

 witness to its ancestry ; while a snail which 

 is not operculated will of course show no 

 tendency to develop such a structure, and so 

 will equally give a true testimony as to its 

 origin. In short, the less functionally useful 

 any organ is, the higher is its value as a 

 gauge of its owner's pedigree, like a Bourborr 

 nose or an Austrian lip. 



