Rau—O bservations on Samia Cecropia, Linn. 43 
slow decline. The Cecropia moth has about enough vital- 
ity to fertilize one female; after that its longer or shorter 
life is of no consequence to the species. 
Seeing the similarity between the duration of life and 
the functionless proboscis in Aglia tau and Samia cecro- 
pia, are we not justified in supposing that Aglia tau is 
also monagamous, and that the longer duration of life of 
the male of Agha tau is one of slow decline and that 
physically it is unfit to fly actively about after impregna- 
tion? 
If we suppose Weismann to mean that Aglia tau flies 
swiftly through the forests before mating, we must con- 
clude that the species is monagamous. If the species is 
monagamous, and if the females reject old or middle-aged 
males, as they do in the cecropia, and considering the 
physical condition of a moth that has flown through the 
forests without nourishment for from eight to fourteen 
days, we can well see how necessary it is for mating to 
take place while the males are quite young. If it is 
necessary for the male to mate when very young, in what 
way can a useless life of the male from 8 to 14 days 
benefit the race? 
Weismann states that his notes on the life of Aglia tau 
are not from direct observation, but are estimated from 
the time when these insects were seen on the wing. It 
might be possible that further observations on Aglia tau 
would show that the duration of its life and its habits are 
somewhat similar to that of Samia cecropia. 
(b) Conclusions. 
Finding the duration of life of the female to be in- 
sufficient to propagate the race to its fullest extent, and, 
in contrast to this, an excessive duration of life in the 
male, which in a species that is monagamous can be noth- 
ing but useless, we must conclude that the duration of 
life at this stage of evolution cannot be an adaptation 
for the good of the species. 
Perhaps the male lives longer because it can accumu- 
late larger stores of reserve nutriment in the larval 
