branous collarette in the form of a funnel. All these characters are found in the Codosigœ, monocellular Infusoria, always living isolated, and are to the sponges what the Hydras are to the Siphonifera and Coral Polyps. In the Anthophysœ these cellules live in colonies, but are yet all alike. Let polymorphism step in. Let some of the associated
Fig. 16.—a, and b, Amoebæ, c, d, e, sponge particles.
cells preserve the flagelliferous form, while others become amoebae, a transformation which is possible, since it constitutes one of the most frequent modes of reproduction of the amoeboid Infusoria, and the Anthophysa is transformed into a sponge. The process is always the same, whatever the nature of the assembled materials. Cells or polyps, it always submits to the same elaboration in developing new individuals. The cells, once assembled in the organism, yield easily to the changes required by the division of physiological labor, and form various organs, although these organs never become true individuals. If the individuals of a colony often descend to the state of organs, we must not conclude that the organs of an animal are always individuals that have lost their autonomy; but the animal to which they belong, though it may never have been an assemblage of individualities intermediate between its own and that of cells, is not less a colony of the latter subjected to the laws of evolution of all the others. Thus even if we can not prove that Vertebrates and Mollusks have resulted from the fusion of more simple beings that have lived an independent life, they are still colonies of cells, and the law of association has consequently lost none of its generality.
It remains the fundamental law of development in the animal kingdom, comprehending and controlling those laws of growth, of organic repetition, of economy, which have been long accepted by physiologists, explaining hitherto mysterious homologies between different parts of the body, or between different organs of the same animal; embracing in one circle all the forms of asexual generation, which are its most powerful means of creation. Resting upon the law of the division of physiological work, the importance of which was first demonstrated by Milne-Edwards, and upon that of polymorphism, which without it have only a limited and indefinite meaning, consequent on the law of division of protoplasmic masses, it has been the great producer of organization, and establishes a new link between
