6o THE DURATION OF LIFE. [I. 



die after fertilizing the females ; while the latter then take to a 

 parasitic life, produce eggs, and continue to live for some time. 

 It is supposed that the dwarf male of Bonellia viridis does not 

 live so long by several years as the hundred times larger 

 female, and it too has no mouth to its alimentary canal. These 

 examples might be further increased by reference to zoological 

 literature. 



In most cases the female lives longer than the male, and this 

 needs no special explanation ; but the converse relation is con- 

 ceivable, when, for instance, the females are much rarer than 

 the males, and the latter lose much time in seeking them. The 

 above-mentioned case of Aglia tau probably belongs to this 

 category. 



We cannot always decide conclusively whether the life of one 

 sex has been lengthened or that of the other shortened ; both 

 these changes must have taken place in different cases. There 

 is no doubt that a lengthening of life in the female has arisen 

 in the bees and ants, for both sexes of the saw-flies, which are 

 believed to be the ancestors of bees, only live for a few weeks. 

 But among the Strepsiptera the shorter life of the male must 

 have been secondarily acquired, since we only rarely meet 

 with such an extreme case in insects. 



Note 7. Bees. 



It has not been experimentally determined whether the 

 workers, which, are usually killed after some months, would 

 live as long as the queen, if they were artificially protected 

 from danger in the hive ; but I think that this is probable, 

 because it is the case among ants, and because the peculiarity 

 of longevity must be latent in the egg. As is well known, the 

 Qgg which gives rise to the queen is identical with that which 

 produces a worker, and differences in the nutrition alone decide 

 whether a queen or a worker shall be formed. It is therefore 

 probable that the duration of life in queen and worker is poten- 

 tially the same. 



Note 8. Death of the Cells in higher Organisms. 



The opinion has been often expressed that the inevitable 

 appearance of normal ' death ' is dependent on the wearing out 

 of the tissues in consequence of their functional activity. Bertin 



