LONGEVITY IN SATURNIID MOTHS 181 
indefinitely, but because the power of multiplying indefinitely was 
lost when it ceased to be of use. 
In answering the question (continues Weismann, loc. cit., p. 20), as 
to the means by which the lengthening or shortening of life is brought 
about, our first appeal must be to the process of natural selection. 
Duration of life, like every other characteristic of an organism, is sub- 
ject. to individual fluctuations. . . . As soon as the long-lived 
individuals in a species obtain some advantage i in the struggle for exist- 
ence, they will probably become dominant and those with the short- 
est lives will be exterminated. 
Lankester,’ according to Romanes, has pointed out ‘‘a highly 
remarkable correlation between potential longevity in the indi- 
vidual and frequency of parturition.” ‘‘This correlation he 
attributes to generative expenditure acting directly to the cur- 
tailment of life.” 
Romanes,‘ who like Weismann sees in the duration of life an 
adaptation, does not agree with Lankester that it is the genera- 
tive expenditure “that causes the curtailment of life, but that 
it is the curtailment of life by Natural Selection, which causes 
the high generative expenditure within the lessened period.”’ 
In opposition to the utilitarian theory of Weismann is that of 
Gotte,® that 
5 4 Gaedeane all animals are mortal, and reproduction is in itself the 
cause of death. Reproduction in Protozoa is preceded by encystation. 
In this condition the organism passes into a non-living condition, from 
which it revives with renewed youth and renewed life; a similar condi- 
tion occurs in the egg of Metazoa, during a certain period in which it 
forms an unorganized, non-living body, composed of organic substances. 
Eimer’s® own opinion is that in the Metazoa as well as in the 
Protozoa the germ cells are immortal; only the soma dies. 
“The latter is not really an end in itself, but rather its principal furc- 
tion is to ensure the maintenance of organic life, by favoring reproduc- 
tion, by sheltering the germ-cells till their maturity, and in order to 
deposit them repeatedly; further, by the dispersal of the same in space, 
2FOCarclite ps 20s 
3 Comparative Longevity, 1870, quoted by Romanes, Monist, vol. 5, p. 168, 
1895. 
4 Monist, vol. 5, p. 163, 1895. 
® Quoted by Eimer, Organic Evolution, p. 67, 1890. 
5 Loc. cit., p. 68-69. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, NO. 2 
