65:2.2

Very few species of the early types of marine vegetation that participated in those epochal changes which resulted in the animallike borderland organisms are in existence today. The sponges are the survivors of one of these early midway types, those organisms through which the gradual transition from the vegetable to the animal took place. These early transition forms, while not identical with modern sponges, were much like them; they were true borderline organisms—neither vegetable nor animal—but they eventually led to the development of the true animal forms of life.