4 THE DURATION OF LIFE. 



upon the conditions of life in these animals ; hence in this case we 

 can directly examine the factors upon which, as I believe, the dura- 

 tion of life is chiefly based. Sir John Lubbock in England, and 

 Dr. August Forel of Zurich, have had the kindness to send me 

 an account of their observations upon ants, and S. Clessin of 

 Ochsenfurth his researches upon our native land and fresh-water 

 Mollusca. 



In publishing- these valuable communications, together with all 

 facts which I have been able to collect from literature upon the 

 subject of the duration of life, and the little which I have myself 

 observed upon this subject, I hope to provide a stimulus for 

 further observation in this field, which has been hitherto much 

 neglected. The views which I have brought forward in this paper 

 are based on a comparatively small number of facts, at least as far 

 as the duration of life in various species is concerned. The larger 

 the number of accurate data which are supplied, and the more 

 exactly the duration of life and its conditions are ascertained, the 

 more securely will it be possible to establish our views upon the 

 causes which determine the duration of life. 



A. W. 



NAPLES, Dec. 6, 1881. 



