OF WASHINGTON. 109 



writings, that death has resulted in the evolution of life, not as an 

 abstract necessity, but as an adaptation an incident beneficial to 

 the species through the agency of natural selection. It has been 

 found more useful to the species that the individual shall perish 

 and perpetuate the type in its offspring than for the individual 

 continuously to exist, death being in one respect the instrumen 

 tality which nature has employed to produce an infinite variety of 

 forms and an increased complexity of structure which the past 

 and present history of life upon our planet exemplify. In short, 

 while death has almost universally been looked upon as inherent 

 in organic nature, Weismann, to use his own words, believes that 

 this explanation is invalid, and considers death not as a primary 

 necessity, but as an adaptation secondarily acquired. The un 

 limited existence of individuals would be a luxury without cor 

 responding advantage, and the power of multiplying indefinitely 

 was lost when it ceased to be of use. 



It is not my purpose in this connection to discuss the deeper 

 question of the necessity or non-necessity of death in the abstract ; 

 for, however ingenious Weismann's presentation of this part of 

 his subject may be, most persons will accept his own conclusion 

 that the problem is, for the present, insoluble, and that it is the 

 quest after perfected truth, not its possession, that falls to our lot. 

 Upon the second phase of the problem, as to whether the dura 

 tion of individual life has been regulated by the conditions sur 

 rounding, and the necessities of, the species, there are numerous 

 facts in nature which seem to justify the theory ; also many 

 which seem to disprove it and to indicate that other factors have 

 been concerned in regulating such individual life. In the data 

 given in his notes Weismann draws very largely from entomology, 

 and a brief consideration of the subject of the duration of life in 

 insects, and of its bearing on the views indicated, may prove 

 profitable and suggestive, and permit me to introduce some un 

 published facts in the life-history of what is generally conceded 

 to be our longest-lived North American species, viz., Cicada 

 septendecim Linn. 



Weismann brings together a series of the best established facts 

 which he has been able to gather, making no claim, however, to 

 have included even most of those which are scattered through 

 the enormous mass of entomological literature. He purposely 

 confines his consideration to the life of the imago or adult insect, 

 /. <?., the reproductive state, though I think that by so doing he 

 very materially lessens the value of his data as bearing on his 

 theories, especially as in other classes of animals he includes the 

 whole life of the individual. The life of the larva should not 

 be excluded. Neither does he reckon the time spent in the torpid 

 condition, believing that it should not be reckoned with the active 



