LIVING MILLSTONES 



THE mill-like action of their own upper and lower molar- 

 teeth upon one another may have been quite sufficient to 

 suggest to our prehistoric parents the idea of opposing a 

 pair of corrugated stones in such a manner that by mutual 

 rotation or revolution they should be capable of reducing 

 to powder hard substances placed between them. Indeed, 

 the idea of millstones is such a simple and natural one 

 that it is quite probable it may have occurred to the human 

 mind without any reference to any prototype in nature ; and 

 in any case, if such a natural prototype is to be sought, it 

 is not necessary to go farther in search of it than our own 

 dental organs. Excellent, however, for their special purpose 

 as are these organs (when not subject to premature decay), 

 there are other types of tooth-structure to be met with in 

 the animal kingdom which present a much closer approxima- 

 tion to millstones, and might well have foreshadowed these 

 instruments, had they only been accessible to the primeval 

 savage. But since these natural millstones occur only in 

 marine fishes, some of which inhabit distant seas, while 

 others are met with only as fossils, deeply buried in the 

 rocks, it is evident that the idea of artificial millstones 

 is not derived from these natural prototypes. In other 

 words, to use an expression now fashionable in natural 

 science, the development of artificial and natural millstones 

 is a case of parallelism. 



