514 THE PHILOSOPHY 



in the moft fatisfailory manner. He even mentions one which he 

 fuppofed to be two hundred years old *. Two methods have been 

 devifed for afcertaining the age of fifties, namely, by the circles of 

 the fcales, and by a tranfverfe feftion of the back-bone. When a 

 fcale of a fifli is examined by the microfcope, it is found to confift 

 of a number of circles within one another, refembling, in fome mea- 

 fure, thofe rings that appear on the tranfverfe fedions of trees, by 

 v/hlch their ages are computed. In the fame manner, the ages of 

 fifties may be afcertained by the number of circles on their fcales, 

 reckoning for each ring one year of the animal's exiftence. The 

 ages of BufFon's carps were chiefly determined by the circles on their 

 fcales. The age of fifties that want fcales, as the flcate and ray-kind, 

 may be pretty exactly known by feparating the joints of the back- 

 bone, and obferving minutely the number of rings which the furface 

 exhibits. Both of thefe methods may be liable to deception ; but 

 they are the only natural ones which have hitherto been difcovered. 

 The longevity of fifties has been afcribed to feveral caufes. The 

 element in which they live is more uniform, and lefs fubje£t to ac- 

 cidental changes than the air of our atmofphere. Their bones, 

 which are more of a cartilaginous nature than thofe of land animals, 

 admit of indefinite extenfion ; of courfe, their bodies, inftead of 

 fuiTering the rigidity of age at an early period, which is the natural 

 caufe of death, continue to giow much longer than thofe of moft 

 land animals. 



As to the age of Reptiles, probably from the uninterefting nature 

 of the animals, we have very little information. But two letters of 

 J. Arfcott, Efq; of Tehott in Devonftiire, concerning the longevity 

 of a toad, deferve fome notice. Thefe letters were addrefied to Dr 

 Milles, Dean of Exeter, and by him communicated to Mr Pennant 



in 



* Epoques de la Nature, pag. i8i. 



