of the same kind, as the word is occasionally used, but the struggle with the whole of nature. Nature is in continual movement, and is always changing her forms, hence only such individuals are able to maintain their form for any period of time in this eternal change who are in a position to develop particular organs against those external influences which threaten the existence of the individual, as well as to supply the places of those parts which it is obliged to give up continually to the external world. Quickest and best will those individuals and groups assert themselves whose weapons of defence and instruments for obtaining food are the best adapted to their end, that is, best adapted to the external world: to avoid its dangers and to capture the sources of food. This uninterrupted process of adaptation and selection of the fittest by means of the struggle for existence produces, under such circumstances as usually form themselves on the earth since it has borne organised beings, an increasing division of labour. In fact, the more developed the division of labour is in a society, the more advanced does that society appear to us. The continual process of rendering the organic world more perfect is thus the result of the struggle for existence in it, and probably for a long time to come will be its future result, as long as the conditions of our planet do not essentially alter. Certainly we have no right to look on this process as a necessary law for all time. That would amount to imputing to the world an end which is not to be found in it.
The development need not always proceed at the same rate. From time to time periods can come when the various organisms, each in its way, arrive at the highest possible degree of adaptation to the existing conditions, that is, are in the most complete harmony with their surroundings. So long as these conditions endure they will develop no farther, but the form which has been arrived at will develop into a fixed type, which procreates itself unchanged. A further development will only then occur when the surroundings undergo a considerable alteration: if when the inorganic nature is subject to changes which disturb the balance of the
