88 DEUXIÈME ASSEMBLÉE GÉNÉRALE 
palæogeography is that which constantly animates the older as well as 
many of the younger workers in this field. 
Zoological methods. — Zoology in the sense of studying extinct forms 
as living organisms is also becoming closer day by day, and we are now 
enjoying the recognition by mammalogists (Weger ‘!, Bepparp*) of the 
absolute necessity of coupling the study of ancestral with that of the 
recent forms in al] questions both of distribution and of classification. 
In connection with distribution our chief advance has been to determine 
the exact geographical location and chronological succession of animals, 
the local conditions of geological deposition in relation to habits and ha- 
bitat or environment, as well as its bearing upon the study of past cli- 
mates, or what may be called palæometeorology. 
Adaptive radiation, continental. — In connection with the comparison 
of mammals in their intercontinental as well as in their continental re- 
lations, the branching system of Lamarcr and the divergence which 
impressed Darwin is perhaps most clearly expressed by the word « ra- 
diation »*. Elsewhere the conception of adaptive radiation has been fully 
developed in connection with the origin of certain orders‘. 
It may here be briefly pointed out that Africa ”, South America, North 
America and Eurasia prove to have been the three chief geographical 
centres of ordinal radiation. 
Adaptive radiation, local®.— Quite as important, although not carried 
on so grand a scale, is the local adaptive radiation which brings about 
a diversity of type in the same geographical regions and is the basis of 
the polyphyletic law of which we shall next speak. It is perhaps best 
illustrated by the Ungulates. In addition to (1) digital reduction (Kowa- 
LEVSKY) and (2) carpal and tarsal displacement (Cope, OsBorN) in relation 
to the choice of harder and softer ground, there is recognized (3) after the 
primary conversion of semi-Unguiculate into Ungulate types, a reversed 
conversion of Ungulate types into clawed types, as seen in Dichobune 
(Artiodactyla), Chalicotherium (Perissodactyla), and perhaps in an inci- 
pient stage in Agriochærus (Artiodactyla) ;: (4) secondary adoption of 
aquatic habits, as seen, for example, in the Amynodontidæ among the Rhi- 
! Die Sûüugethiere. 8°, Jena, 1904. 
? Mammalia. The Cambridge Natural History, 8°, 1902. 
% OsBoRN, H. K., Rise of the Mammalia. Proc. Amer. Association. Adv. Sc. Vol. 
xlii, 1593, p. 215. 
* Adaptive Radiation of Orders and Families. Ann. N. Y. Acad. Sei. Vol. xiii. 
1900, pp. 49-51. 
5 Ann. N. Y. Acad. Sci. XIII, 1900, pp. 56-58. 
5 Oseorx, H. F. The Law of Adaptive Radiation. Amer. Nat. xxxvi, 1902, 
pp. 353-565. 
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