A sketch of contributions made from studies on sponges to some of the larger ideas of biology, such as the existence of evolutionary series; the cellular structure of animals; the presence in an adult of totipotent cells; the compensatory development in a degenerating organism of regenerative masses; the viability of cells after removal from the body and the possibility of such cooperative action between them as would result in the restoration of a body; the question as to the occurrence of a cellular dedifferentiation leading back to a regenerative state; and the possibility that embryogenic variation may sometimes be due to self-adaptation.