migratory and in time will become so well adapted to local condi¬ 
tions that migration will cease. This bold conception of the case 
loses significance when it is remembered that all the evidence from 
embryology, comparative anatomy and palaeontology points un¬ 
mistakably to the conclusion that birds have arisen from reptile¬ 
like ancestors of the crawling or lizard type and not from the 
flying or pterodactyl type, and, moreover, that the art of flying 
was a gradual acquisition which had by no means reached the per¬ 
fection in Tertiary times which Graser’s theory presupposes. 
The Deichler- Another ancestral-habit theory, known as the 
Jager Theory Deichlei'-Jager theory after its proposers, lays 
particular emphasis upon the role played by the glacial period 
toward the end of Tertiary times. There is geological evidence 
that during the pleistocene period at least three distinct glacial 
ages occurred one after the other, during which the present tem¬ 
perate regions of the earth were slowly invaded by an encroaching 
polar sheet of ice until they became quite uninhabitable except by 
arctic organisms. Before and between these glacial ages modern 
temperate regions swung to the tropical extreme in character 
which is proven by the discovery of fossil ferns as far north as 
Greenland. The Deichler-Jager theory assumes that birds as a 
class in all probability arose from reptile-like ancestors during Ter¬ 
tiary'- times and that their original home was in the north. So long as 
the climate remained essentially tropical throughout the year there 
was no occasion for deserting this area. With the gradual advent 
of the first glacial age, however, the climate of the north slowly', 
changed from being tropical the year around to a condition of sea¬ 
sonal changes somewhat similar to that obtaining today. When 
these seasonal changes became extreme tropical conditions were 
interrupted and the first winter occurred. There is no reason to 
believe that this first winter was either sudden or severe but, in 
the course of time, it became an established annual occurrence and 
was finally much more severe than our winters at present, as has 
been demonstrated by the occurrence of fossil reindeer bones in 
France and arctic musk-oxen as far south as Kentucky. 
Now when organisms of any locality are overtaken by winter 
one of these results may occur; first, they may simply perish; sec¬ 
ond, they may hibernate through the cold weather in a semi-tor- 
pid condition, or finally, they may migrate to a more favorable 
environment. Birds, being endowed with the power of locomotion 
through the air pursued the latter alternative and thus the fall 
migration had its origin. Every spring as the advance of the gla¬ 
cial sheet relaxed for a season the birds which had been driven 
south into crowded quarters by the rigors of winter temporarilv 
