AN OUTLINE OF THE THEORY. 21 
various animal types is asserted to imply a community of 
descent. “Large groups of species, whose habits are 
widely different, present certain fundamental likenesses of 
structure. The arms of men and apes, the fore-legs of 
quadrupeds, the paddles of whales, the wings of birds, 
the breast-fins of fishes, are constructed on the same pat- 
tern, but altered to suit their several functions. Nearly 
all mammals, from the long-necked giraffe to the short- 
necked elephant, have seven neck-bones; the eyes of the 
lamprey are moved by six muscles which correspond ex- 
actly to the six which work the human eye; all insects and 
crustacea—moth and lobster, beetle and cray-fish—are 
alike composed of twenty segments; the sepals, petals, 
stamens, and pistils of a flower are all modified leaves 
arranged in a spire.” ‘(Clodd, “The Story of Creation,” 
p. 102.) These resemblances are looked upon as evidence 
of a common origin. 
b) The Argument from Embryology. The indivi- 
dual animal in embryonic development passes through 
temporary stages which are similar to permanent condi- 
tions in some of the lower forms in the same group. 
Evolutionists believe that these forms were actually pos- 
sessed by the ancestors of these animals in the course 
of their evolution. They hold that the changes which 
take place in the embryos epitomize the series of changes 
through which the ancestral forms passed. Because the 
embryos of some four-footed animals have gill-slits, this 
is pointed out as evidence that land animals are evolved 
from fishes. 
c) Geographical Distribution. In geological time, 
natural barriers have sprung up which separated the 
species which have since developed. In this way the ex- 
istence of marsupials (pouched animals—kangaroo, op- 
possum) on certain limited areas, the limitation of certain 
plants to certain islands, etc., are explained. 
