NOVEMBER, 1905. OECOLOGICAL FEATURES OF EVOLUTION. 
171 
in the environment of the predatory form and conversely if it 
finds forms in the new region which it preys upon they become 
elements of hospitality in its environment. So complex are the 
relations that the introduction of an element of hostility to one 
form may result in an increase of hospitality to another as when 
a predatory form abandons the refuse of its meal to the carrion 
feeders. Darwins classic example of the relation between the 
number of cats and the clover crop of a neighborhood is a case 
in point. 
Passive hostility of the environment from animals is almost 
if not quite the same as the hostility of inanimate things. The 
competition for food, breeding places, etc., among different forms 
and among individuals of the same species ; it involves the 
struggle for existence among life forms. 
II. From contacts other than animal. Under this head must 
be grouped a large series of contacts which can only be suggested 
within the limits of this article. Climate, this may be favorable 
or unfavorable to the new form in its tendency to drought, 
humidity, great range of temperature or stability of temperature. 
Surface, the rough or broken surface, hills, plains, plateaus or 
swamps ; each would afford peculiar possibilities for or against 
food, protection, breeding places, etc. Rocks and soils, affording 
facilities of burrowing, etc. Hydrtographic features as rivers, 
lakes, each carrying its aid or opposition to the new comer. The 
list might be extended almost indefinitely but would have to be 
varied for each form and almost for each individual. 
Should the animal encounter conditions of hostility in its new 
environment its only chance for survival would be the develop- 
ment of new structures or habits that would enable it to use more 
or fewer than the original contacts or be able to use or resist the 
originally hostile contacts in such a way as to alter their effect 
from hostility to hospitality. 
At this point another element must be considered, that of 
time. This element is worthy of rather more consideration than 
it has already received. The assumption of unlimited time is one 
that paleontology has inherited from its foster-mother geology 
and the assumption has also tinged the writings on recent 
zoology. The form in an hostile environment has but two goals 
before it, adaptation or extinction. That the latter has been com- 
monly attained we have ample evidence. The change in the en- 
vironment which renders it hostile to the animal may be sudden 
or very slow. In the former case the animal has small chance for 
survival. Such a case would be the introduction by migration of 
