The simplest beings habitually multiply by spontaneous fission. Physical altruism of the lowest kind, differentiating from physical egoism, may, in this case, be considered as not yet independent of it. For since the two halves which, before fission, constituted the individual, do not on dividing disappear, we must say that though the individuality of the parent infusorium or other protozoon is lost in ceasing to be single, yet the old individual continues to exist in each of the new individuals. When, however, as happens generally with these smallest animals, an interval of quiescence ends in the breaking up of the whole body into minute parts, each of which is the germ of a young one, we see the parent entirely sacrificed in forming progeny. Here might be described how among creatures of higher grades, by fission or gemmation, parents bequeath parts of their bodies, more or less organized, to form offspring at the cost of their own individualities. Numerous examples might also be given of the ways in which the development of ova is carried to the extent of making the parental body little more than a receptacle for them: the implication being that the accumulations of nutriment which parental activities have laid up, are disposed of for the benefit of posterity. And then might be dwelt on the multitudinous cases where, as generally throughout the insect-world, maturity having been reached and a new generation provided for, life ends: death follows the sacrifices made for progeny. But leaving these lower types in which the altruism is physical only, or in which it is physical and automatically psychical only, let us ascend to those in which it is also, to a considerable degree, conscious. Though, in birds and mammals, such parental activities, as are guided by instinct, are accompanied by either no representations or but vague representations of the benefits which the young receive, yet there are also in them actions which we may class as altruistic in the higher sense. The agitation which creatures of these classes show when their young are in danger, joined often with efforts on their behalf, as well as grief displayed after loss of their young, make it manifest that in them parental altruism has a concomitant of emotion.