Page:The Effect of External Influences upon Development.djvu/45

Rh on a metamorphosis of the homologous determinants of all the ids, but only of a small majority of them, which would just be sufficient to cause the development of the altered character. The number of ids thus modified increases gradually by the. aid of the processes of amphimixis and reducing division; and simultaneously a change occurs in the determinants of other cooperating parts of the body, until finally most or all of them are modified in some respect—sometimes in a lesser, sometimes in a greater degree. Thus the ids in question take on an entirely new nature.

This process is the same as that conceived to occur in the formation of the workers of ants and bees—with the one difference that among these there could never be a conversion of all or even of most of the ids into 'worker-ids,' but only a definite percentage of them; for the fertile females continued to be necessary for the species, and so had to be represented by a number of ids in the germ-plasm. But in the ordinary metamorphosis of a species some of the ids, if my theory is correct, will always be retained for a long time unchanged or but little changed: this we may conclude to be the case from the phenomena of reversion. Such unaltered ids, having ceased to be important for the species, may gradually disappear by means of the reducing divisions, till at last only isolated groups of old determinants are retained in a few of the ids. But in the case of the social insects a relationship has become established between old and new ids; and this we can only ascribe to processes of selection.

If in the germ-plasm of the bee there were only one