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BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 3, NO. 4. 
a predatory form as the introduction of the hunter with his gun, 
into regions previously unvisited. The burning of forests and 
prairies ; volcanic eruptions, etc., would have only a very local 
effect, upon species of limited distribution, upon varieties or 
races and even on individuals. But the clearing off of the estab- 
lished forms may open the way for the introduction of migrant 
forms ; this is especially well illustrated in the occupaton of burnt 
over lands by the new forms of plant life. In every case swift 
extinction will follow if the animal does not produce chaneed 
form or habit fitted to the changed environment. If the neces- 
sary change is one involving habit the possibilities of the animal 
responding in time to avoid extinction are greatly increased but 
this depends in a large measure on the potential variability of the 
animal ; the seals return year after year to the same breeding 
place and to almost certain extinction. The English Sparrow on 
the other hand has developed familiar habits and breeds on the 
structures that man has erected in place of the destroyed forest. 
The chimney swallow has accepted the chimney in place of the 
hollow tree and the work of man has become an element of hospi- 
tality in their environment. The birds mentioned have developed 
habits in time to profit by the changed environment, it is doubt- 
ful if the seal will do so. 
Adaptations in structure or function would require a much 
longer time and could not possibly win out against any sudden 
change but might do so through the long time involved in 
changes due to geological development of changed land surfaces 
and climates. This last statement must not be interpreted to 
mean that a suddenly developed new form as one of DeVries 
primroses or any sport that becomes established would neces- 
sarily encounter environmental hostility at the beginning ; for the 
new structure, function or habit might, in the rare instances when 
such a form is established, present a peculiar combination of char- 
acters that will enable it to seize upon a hitherto unoccupied 
group of contacts and so experience environmental hospitality 
from the start, although the parent stem from which it developed 
was also in the same state; much the larger number of the varia- 
tions however, would experience a hostility so great as to cause 
extinction. 
Such is the course of ordinary morphological development 
following the changes of the environment and the plentiful in- 
stances of extinction are ample evidence that the failure of animal 
forms to produce their change in time has been no inconsidera- 
ble factor. It is not presumed that given sufficient time anv form 
