10 
ANNALS NEW YORK ACADEMY OF SCIENCES 
H 
GEOGRAPHICAL DISTRIBUTION 
Few organisms occur uniformly throughout the various continental areas 
of the earth. In general, land types differ more or less widely according to 
the degree of proximity of the areas where they occur, and their differences 
are usually regarded as due to their adaptation to the unlike natural condi¬ 
tions of different areas. 
Illustrations 
1. Specimens of the larger fungi as examples of invariable boreal 
and tropical plants. 
2. The Land Tortoise of the Galapagos Islands, a form which is 
peculiar to this entirely isolated group of islands. 
3. Several kinds of Ground-Squirrels from different localities in the 
United States. 
4. Land Snails from valleys of the Society Islands, in the South 
Pacific Ocean. Each island possesses characteristic forms, 
and the different valleys of one and the same island often 
contain unique forms. 
I 
PRINCIPLES OF CLASSIFICATION 
Resemblances displayed by different species of animals and plants are 
regarded as indications of common ancestry. It is therefore possible to 
classify organisms in a tree-like diagrammatic manner, into larger and 
smaller groups according to their fundamental similarities. The principle 
seems to be universal for all plants and all animals. 
Illustrations 
1. Living specimens of Cactus plants. 
2. A typical series of Crustacea. 
J 
PRINCIPLES OF HOMOLOGY 
Parts of organisms presenting the same fundamental plan of construction, 
though they differ in function, are spoken of as “homologous/' 1 
