92. Let the social organism furnish us with an illustration. At the present moment there is a movement against the retail shopkeepers of London in favor of Co-operative Stores. The stimulus of getting better goods and cheaper, attracts the flow of custom from its old channels; and if this continue a certain time the new arrangements will be so thoroughly organized, and will work so easily, that Co-operative Stores will to a great extent supplant the retail shops. But if from any causes the stimulus slackens before this reorganization has passed from the oscillating into the permanent stage--if the goods are not found to be superior, or the cheapness not worth the extra trouble--the old influences (aiding our indolence) which have been long and continuously at work, will cause the social organism to resume its old aspect, and the co-operative “varieties” will disappear, or exist beside the ancient “species.” In the one case as in the other a glance at the process is enough to detect that the increase in the activity has been preceded by a corresponding increase in the structure. The muscle has not been enlarged _by_ extra activity, but _with_ it. The co-operative action has grown with each additional co-operator. Looking at the cases from afar we may justly say that development has been due to function; but looking to the process we see that each increment of activity was necessarily dependent on an increment of substance. When changes of habit or adaptation are said to produce modifications in structures, this is true in as far as one modification of structure necessarily brings with it correlative modifications, the growth of one part affecting the growth of all more or less; but we must remember that to render the structure capable of new adaptations corresponding modifications must have been going on. The retail shopkeepers might securely laugh at the co-operative movement if the respectable families would not or could not become co-operant. When Mr. Spencer urges that “not only may leaf-stalks assume to a great degree the character of stems when they have to discharge the functions of stems by supporting many leaves, and very large leaves, but they may assume the characters of leaves when they have to undertake the functions of leaves,” I would ask if he is not reversing the actual process? The stem cannot assume the functions of a leaf until it has first assumed the character of a leaf. The assumptions of both must be gradual, and _pari passu_.