THE AXA/A/AALS & BIRDS OF NATAL -

CHAPTER XXI

HE following article, specially written for this publication, by Ernest Warren, Esq.. D.Sc. (Lond.). will no doubt be of great interest to many :—

To pass in review the more interesting characters of the fauna or flora of any country it is important that the biological relationships of the country to the surrounding regions should be carefully considered.

In any limited district the distribution of the animals and plants is, as we know, local ; since certain species occur in one part and not in another. Such distribution is dependent on local conditions, as altitude, rainfall, nature of the soil, temperature, and the presence or absence of certain other animals or plants. The causes of the local distribution may be difficult to determine and exceedingly complex; but they are related to the physical and

biological environment.

When, however, we compare the fauna and flora of widely separated regions of the earth's surface we find that they possess a distinct fades which is largely independent of the climatic conditions and biological environment. For example, the climatic conditions of Natal and certain parts of California are closely similar, but the kind of animals found in the two countries is widely different. Here we have a regional distinction in the organic forms, arising through the separation of the countries from each other during prolonged periods of geological time. New genera have been evolved independently in the two regions, and thus the fauna and flora have assumed a distinctive character.

475