INDIVIDUAL AND SPECIES
AN individual can be an animal or a plant. Common observation shows that the definition of the word individual should be simple, e.g. dog, shark, rose-bush, beech-tree, etc. Nevertheless, sometimes insuperable doubts arise when we try to define what individuality is. Since all living organisms are formed from cells, since there are some plants and animals in existence composed of one cell only, whilst others are combinations of several different cells generally great in number, it is at times difficult if not impossible to distinguish a colony of several single-celled individuals from a polyplastid. We have already alluded to this point.
Hertwig in 1894 defined the individual organism as a living unit capable of preserving its shape, endowed with the general functions of existence, and able to retain its stability or constancy despite variations in the surrounding medium. Individuality may then be defined by its power of making, preserving, rebuilding and reproducing a particular shape or form. It is all the same whether we are dealing with a single-celled organism or one of the more outstanding plants or creatures in this world. A part of an animal or of a plant which goes on living for a period after it has been detached from the main body will not become a fresh individual unless it is able to reconstruct a complete animal or plant identical to the one from which it had its origin.
The individual will therefore exist and produce fresh individuals by reproduction, whatever may be the process by which such reproduction is effected, and will follow a course in time, which is life in its various succeeding stages all exactly mapped out until the end comes in death. Individuality may be said therefore, from the morphological and functional standpoint, to be a complete whole in itself, which in the case of mankind is subjectively translated into consciousness, feeling, and knowledge of the ego. It is through anatomy, physiology and psychology that the individual becomes apart from the world, and opposes himself to his surroundings, forming thus an independent