4 THE DURATION OF LIFE. 



with butterflies. Dr. Adler of Schleswig sent me data upon 

 the duration of Hfe in Cynipidae, which have a special value, as 

 they are accompanied by very exact observations upon the 

 conditions of life in these animals ; hence in this case we can 

 directly examine the factors upon which, as I believe, the 

 duration 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 httle 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 con- 

 cerned. 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. 



