Exactly the same thing occurs in the case of the organic environment, to which each species must also be well adapted in order to live. The two great essentials for animal existence are, to obtain abundant food through successive years, and to be able to escape from their various enemies. When food is scarce the strongest, or those who can feed quickest and digest more rapidly, or those that can detect food at greater distances or reach it more quickly, will have the advantage. Enemies are escaped by strength, by swiftness, by acute vision, by wariness, or by colours which conceal the various species in their natural surroundings; and those which possess these or any other advantages will in the long run survive. The weaker, the less well-defended, and the smaller species often have special protection, such as nocturnal habits, making burrows in the earth, possessing poisonous stings or fangs, being covered with protective armour; while great numbers are coloured or marked so as exactly to correspond with their surroundings, and are thus concealed from their chief enemies. _Natural Selection, or Survival of the Fittest_ It may be here noted that the term "Natural Selection," which has often been misunderstood, was suggested to Darwin by the way in which almost all our varieties of cultivated plants and domestic animals have been obtained from wild forms continually improved for many generations. The method is to breed large quantities, and always preserve or "select" the best in each generation to be the parents of the next. This method, carried on by hundreds of farmers, gardeners, dog, horse or poultry breeders, and especially by pigeon-fanciers, has resulted in all those useful, beautiful and even wonderful varieties of fruits, vegetables and flowers, dray-horses and hunters, greyhounds, spaniels and bull-dogs, cows which give large quantities of the richest milk, and sheep with the greatest quantity and finest quality of wool. All these were produced gradually for the special purposes of mankind; but a similar result has been effected by Nature through rapid increase, great variability, and continual destruction of all the individuals less adapted to the conditions of their special environment, so that only the strongest or the swiftest, the best-concealed or the most wary, the best armed with teeth, horns, hoofs or claws, those who could swim best, or those that protected each other by keeping in flocks or herds—lived the longest and tended to improve still further the next generation. "Survival of the fittest" was suggested by Herbert Spencer as best describing exactly what happens, and it is a most useful descriptive term which should always be kept in mind when discussing or investigating the process by which the infinitely varied and beautiful productions of Nature have been developed. There is really not one single part or organ of any plant or animal that cannot have