124 ENTOMOLOGICAL SOCIETY 



In respect of those insects which require more than one year 

 to undergo their full life-cycle, we have seen that it is very gen 

 erally the rule that the long-lived period is the larval, and that 

 the duration of the imago, pupa, and egg states is relatively brief. 

 This general rule has no exceptions of consequence that I can 

 recall. Nevertheless, within the same genus, and particularly 

 within the same family, different species vary greatly in the period 

 of individual life, and this, too, where the habits are essentially 

 similar. 



The one fact that stands forth more prominently than another 

 in this consideration of the subject of longevity among insects is 

 the great variability, not only in the individuals of the species, 

 but particularly in the different species of a given family. We 

 are also impressed with the power of prolonging life in the indi 

 vidual under abnormal conditions which many insects exhibit. 

 The facts of entomology are thus quite significant in their ap 

 plication to Weismann's views as to the influence of natural 

 selection on the duration of individual life, and few will question 

 the general conclusion that the length of life has, in the main, 

 been fixed in each case by the necessities of the species in other 

 words, it is, as Weismann has argued with the higher animals, 

 very largely dependent on the necessities of life. 



This adaptation is more particularly noticeable in the compen 

 satory adjustments between the lengths of life in different states 

 of the individual development, and in this particular Weismann, 

 as I have already hinted, is weak in confining his attention to 

 the life of the adult, because it is in contemplating the whole 

 life-cycle that he might have found his strongest support for the 

 theory that natural selection has, in the main, influenced lon 

 gevity. For nothing is more certain than that, with insects, 

 where, as is more often the case, the vicissitudes of the imaginal 

 life are such as to make it precarious, we find it to be brief, with 

 a correspondingly lengthened period of larval existence ; whereas, 

 in the rarer cases where the vicissitudes of the active larval life 

 are such as to give great risk to the species, this state is the ab 

 breviated, and either the pupal or imaginal the extended one, in 

 time. 



Thus I am of the opinion that the length of life in insects has 

 been, in the main, regulated by natural selection, acting upon 

 individual variation for the benefit of the species. I say in the 

 main, because I believe that Weismann's chief fault is that he 

 does not sufficiently recognize the limitations of natural selection ; 

 and I believe that the same limitations must be recognized in its 

 application to longevity which have been recognized by myself 



