The geographical distribution of China's fauna and flora may be considered first. One of the main points to note in regard.to this is that animals and plants must be considered in regard to a two-dimensional distribution, each of which affects them more or less profoundly. These are a horizontal distribution and a perpendicular distribution.
To understand the significance of this it is necessary to appreciate the fact that a living organism is very materially affected by, and inevitably reacts to, its environment or surroundings. Whatever else in the theory or evolution may be questioned, this, as a factor in bringing about changes in animal and plant life and the production of new forms, cannot be- disputed. To take an imaginary example. Let it be imagined that a specimen of the most primitive form of animal life, say an amoeba, or a colony of amoebas, is under observation, that it is situated on a continent with hills, mountains, valleys, plains, rivers, streams and lakes, devoid of all life except the simplest unicellular plant forms such as certain algae, and fungi, and that this continent is lying in a sea also containing primitive plant life but nothing else. The continent extends, say, from the Equator to the Arctic Circle, while. the land of which it is formed runs from sea level to an altitude of twenty-five thousand feet. The duration of the observation extends, say, over a few hundred million years. What would be seen?
Naturally the amoebas start out in an aquatic environment, probably in a more or less stagnant pond, where they have all that is necessary to their existence—water, light, oxygen dissolved in the water and food in the form of minute unicellular plants. They thrive and multiply, in time becoming too numerous for their home in the pond. Changes take place. Heavy rains cause the pond to'overflow, and the surplus water finds its way to some nearby stream, taking with it countless amoebas. These are ultimately transported to the rivers and lakes, or even down to the sea, where they find new homes, homes where exist conditions different from: those in the pond. At other times droughts occur, which cause the pond to dry up, shrink away, possibly for a time disappear altogether, leaving the amoebas it contains.dry or buried in the mud. Of at numbers of these weak and perish, but a few survive their new homes or the slight and freakish difference between them and their erstwhile neighbours, possibly as a direct response to the environment. The descendants of those transferred to the Streams, rivers, lakes and ocean, meet with further aquatic adventures; while the descendants of those that survived des-
Sication when the pond dried up begin what may be called a conquest of the land. Sometimes these descendants of the original inhabitants of the pond experience favourable conditions, when they thrive and multiply greatly, establishing themselves firmly: at other times they meet with adverse conditions, or are transported by various agencies to yet other environments, and again there is the struggle for existence and the survival of those which by some freak are better able to withstand the adverse or new conditions, or which are able to respond favourably to the latter.
This spreading will take place in every direction—east, west, north, south, down towards the sea, up towards the mountain tops, and, wherever the organisms go, they will encounter new conditions, which will result in various changes in form, structure, habits and functions taking place in the organisms themselves. Those moving northwards or up the mountain sides will experience greater and greater cold, those moving down towards sea level or southwards, greater and greater heat, and they will change accordingly. After a few millions of years, if a careful survey of the animal life on the continent were to "YOҢ idi tions how important this is. Owing to it animals and plants are distributed according to numerous well defined zones, both horizontally and vertically. The horizontal zones, it will be noticed, run roughly in the direction of the parallels of latitude, seldom in the direction of the meridans of longitude. This is due to the fact that it is warmer towards the equator and colder towards the poles. Strangely enough, it is exactly the same factor that accounts for the few life zones which follow the meridians of longitude. Such north-and-south life-zones are those including the various migrant species of birds, bats, a few insects and certain marine forms such as seals, whales and fishes, which travel north or south with the sun along more or less regular lines of migration.
Text read from the printed page and cleaned; old type leaves the occasional error.