180 PHIL RAU AND NELLIE RAU 
This work falls into the following divisions: The duration of 
life in: 
1. Samia cecropia. 1910—178 insects from St. Louis cocoons. 
2. Samia cecropia. 1911—112 insects from St. Louis cocoons. 
Cocoons placed in incubator. 
3. Samia cecropia. 1911—42 insects from St. Louis cocoons. 
Imagines placed in ice-box. 
4. Samia cecropia. 1911—283 insects from St. Louis cocoons. 
5. Samia cecropia. 1911—133 insects from Long Island 
cocoons. 
6. Callosamia promethea. 1911—170 insects from Creve 
Coeur Lake, Missouri, cocoons. 
7. Tropaea luna. 1911—60 insects from St. Louis and Pike 
County, Missouri, cocoons. 
8. Telea polyphemus. 1911—19 insects from St. Louis and - 
Pike County cocoons. 
REVIEW OF THE THEORIES 
Before taking up the details of the work, it would*be well to 
rehearse here briefly the various theories which have been 
advanced to account for the duration of life. , 
First among these is the theory of Weismann, that the dura- 
tion of life of an organism 
is really dependent upon adaptation to external condi- 
tions, that its length, whether longer or shorter, is governed by the needs 
of the species, and that it is determined by precisely the same mechan- 
ical process of regulation as that by which the structure and functions 
of an organism are adapted to its environment.! 
I consider that death is not a primary necessity, but that it has been 
secondarily acquired as an adaptation. I believe that life is endowed 
with a fixed duration, not because it is contrary to its nature to be 
unlimited, but because the unlimited existence of individuals would be a 
luxury without any corresponding advantage. The above-mentioned 
hypothesis upon the origin and necessity of death leads me to believe 
that the organism did not finally cease to renew the worn-out cell 
material because the nature of the cells did not permit them to multiply 
1 Essays upon Heredity, 2 ed., vol. 1, p. 9, 1891. 
