58 ANATOMY AND PHYSIOLOGY 



might not live and continue to grow for a thou- 

 sand years. 



It was at one time thought that the circles dis- 

 coverable on the ends of the vertebrae of the osse- 

 ous tribes, indicated the age, as the rings on the 

 extremity of a log, marked the years of the growth 

 of the tree. Those, unfortunately, are no guides, 

 and we therefore regret that we know of no 

 mode, at the present day, of solving a problem of 

 the highest interest to the curious. Of the marine 

 fishes, the sharks unquestionably, reach a truly pa- 

 triarchal age. 



SLEEP. 



Exposed as these animals must necessarily be, to 

 the voracious jaws of millions of belligerent, as well 

 as hungry associates, it would seem hardly pos- 

 sible that they should find a safe opportunity for 

 this kind of rest, however much they might at any 

 period require it. Again, being without eye-lids, 

 they would be regarded, at first thought, as organiz- 

 ed to require no suspension of the powers of voli- 

 tion . Impossible as it is to speak with certainty 

 on this point, we are fully persuaded that they not 

 only require sleep, but that they also find safe and 

 convenient times to enjoy that sort of repose. Gold 

 fishes, in vases, repose, regularly through the night, 



