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REV. J. T. GULICK ON DIVERGENT EVOLUTION 
Evolution through Diversity of Use, will operate as surely in the 
one ease as in the other. 
1. Sustentational Segregation arises from the use of different 
methods of obtaining sustentation by members of the same 
species. 
There can be no doubt that of the innumerable cases where 
phytophagic varieties (as they are sometimes called) of insects 
exist, a considerable proportion would be found on investigation 
to be permanent varieties producing offspring that are better 
adapted to the use of the special form of food consumed by the 
parents than are the offspring of other varieties ; and it is evi- 
dent that if the peculiar habits of each variety had no tendency 
to produce segregative breeding this result would not be reached ; 
for each variety would be promiscuously mingled with every 
other, and, though the tendency to variation might be greatly 
increased, the regular production of any one variety of youug 
would be prevented. 
A large mass of facts could be easily gathered illustrative of 
Sustentational Segregation ; but as the principle will probably 
be denied by no one, we shall pass on without further expansion 
of this part of the subject. 
2. Protectional Segregation is Segregation from the use of 
different methods of protection against adverse influences in the 
environment. 
When a new enemy enters the field occupied by any species 
different methods of escape or defence are often open to the 
members of the one species ; and the use of these different 
methods must sometimes result in the segregation of the mem- 
bers according to the methods adopted. Some may hide in 
thickets or holes, wdhle others preserve themselves by flight. 
Supposing the species to be an edible butterfly occupying the 
open fields, and the new enemy to be an insectivorous bird also 
keeping to the open country, certain members might escape by 
taking to the wood-lands, while others might remain in their old 
haunt, gaining through Protectional Selection more and more 
likeness to some inedible species. 
3. Pidificational Segregation. — Let us now consider the effects 
of divergent habits in regard to nest-building. It is well known 
to American ornithologists that the Cliff Swallow of the eastern 
portions of the United States has for the most part ceased to 
build nests in the cliffs that were the original haunts of the 
