INDUSTRIAL ISOLATION. 119 
same is true of the cyclical isolation between two broods of the period- 
ical cicada when occupying the same district.* As each brood lives 
nearly seventeen years burrowing in the ground, and then spends the 
’ few last weeks of its allotted life above ground breeding in the trees, it 
never hasa chance to cross with the other brood, whose time for breed- 
ing comes on another year, and each seventeenth year thereafter.f 
Industrial isolation and migrational isolation, so far as they are deter- 
mined by diversity in the habits or instincts of the members of the 
species, must also be classed as forms of endonomic isolation. 
Heteronomic rsolation.—In the four remaining forms of environal 
isolation, namely, transportational, geological, fertilizational, and 
artificial isolation, heteronomic influences must prevail. 
3. Industrial Isolation. 
Industrial isolation is isolation arising from the activities by which 
the organisin protects itself against adverse influences in the environ- 
ment, or by which it finds and appropriates special resources in the 
environment. 
The different forms of industrial isolation are sustentational, pro- 
tectional, and nidificational isolation. 
For the production of industrial isolation it is necessary that there 
should be, in the same environment, a diversity of fully and of approx- 
imately available resources more or less separated, and in the organ- 
ism some diversity of adaptation to these resources, accompanied by 
powers of search and of discrimination, by which it is able to find the 
resources for which it is best fitted and to adhere to the same when 
found. 
The relation in which these causes stand to each other and through 
which they produce segregation may be described as separation 
according to endowment produced by endeavor according to endow- 
ment. From the nature of the process it produces segregation; for 
those of like aptitudes are brought together. 
It is evident that if initial variation presents in any case a diversity 
of adaptations to surrounding resources that can not be followed 
without separating those differently endowed, we shall have, in the 
very nature of such variation, a cause of segregation and of divergent 
evolution. Some slight variation in the digestive powers of a few 
individuals makes it possible for them to live exclusively on some abun- 
* For a full statement see U.S. Department of Agriculture, Division of Ento- 
mology, Bulletin No. 8, and Bulletin No. 14, New Series, 1898. 
+ For a comparatively full account of the different broods of this species, and 
the problems raised by the remarkable facts, see Appendix II, Sec. III, 3. 
