78 THE POPULAR SCIENCE MONTHLY 
is more than divergence because it implies evolution in every direction 
from a central form. The idea of radii, or radiations from a central 
form greatly assists the imagination, because a distinctive feature of 
paleontology is that we are constantly dealing with fragments of his- 
tory. he radiations which have been discovered must be supple- 
mented by those which remain to be discovered, and it is very remark- 
able how in group after group of animals these missing “ radii” have 
turned up. 
Radiation actually begins in certain single organs, and the first 
principle to be observed, as shown in the accompanying diagram, is 
LIMBS AND FEET 
VOLANT 
FOSSORIAL 
ARBOREAL 
Short-limbed, plantigrade, | AMBULATORY 
pentadactyl, unguicu- OR 
late Stem TERRESTRIAL 
NATATORIAL CURSORIAL 
Amphibious Digitigrade 
Aquatic Unguligrade 
TEETH 
OMNIVOROUS Grass 
Herb 
Fish HERBIVOROUS 2 Shrub 
CARNIVOROUS J Flesh Fruit 
Carrion Root 
MYRMECOPHAGOUS 
fie OO aid Dentition reduced 
OE 
Stem INSECTIVOROUS 
MAIN LINES OF ADAPTIVE RADIATION OF (a) limbs and feet, (b) teeth among mammals. 
