has perished. The yellow pigment, he says, is identical with that of diatoms, and gives the same chemical reactions.
Turning his attention next to the sea-anemones, medusa?, etc., he was equally successful. He is convinced that the pigment-bodies are true algæ and he records this remarkable experiment: "The exposure of a shoal of the beautiful blue pelagic Siphonophore, Velella, for a few hours, enabled me to collect a large quantity of gas which yielded from twenty-four to twenty-five per cent of oxygen. . . . But the most startling result was obtained by the exposure of the common Anthea cereus [sea-anemone], which yielded great quantities of gas, containing on an average from thirty-two to thirty-eight per cent of oxygen." He was able also to prove that this gas came from the associated algæ—specimens destitute of algæ giving off no oxygen whatever.
It is, therefore, now very certain that the yellow cells of radiolarians and the pigment-bodies of cœlenterates are in many cases true alga; living in the animal substance. Geddes's work, when added to that of Cienkowski, the Hertwigs, and Brandt, makes this so clear that we are justified in fully accepting their theory, and in hereafter considering the association of certain chlorophyl-bearing plants with certain animals as an established fact. It has been proposed to apply to this association the term symbiosis, and to designate animals which are thus supplied with algoid messmates as "symbiotic." So much for the "yellow cells" and pigment-bodies of radiolarians and coelenterates. Dr. Brandt, it will be remembered, has expressed his belief that the green-colored Hydra and Spongilla are also symbiotic. In Mr. Geddes's paper nothing is said upon this subject, although, from a remark let fall near the close, it is plain that when the paper was written he did not accept Dr. Brandt's view, but would reserve Hydra, Spongilla, and Convoluta, for a special group of "vegetating animals" distinctly unlike those which are symbiotic.
Professor Lankester, however, while inclined to accept all that has been shown for symbiosis in the other cases, refuses most emphatically to apply that doctrine to Hydra and Spongilla. His dissent is all the more important, because he has paid much attention to the study of animal and plant pigments (especially with the spectroscope); and, because he was the first to establish the presence of chlorophyl in Hydra and Spongilla, he has a special right to be heard in this case. In the paper quoted above he attacks the subject with great vigor, and describes several important experiments tending to show that the green color of Hydra and Spongilla is due to chlorophyl bodies analogous rather to those structures in plants than to any algoid messmates. He fails to confirm Dr. Brandt's observations, and questions the virtue of his inferences so generally, that the two authorities are practically in diametrical opposition. It is obvious that still further studies must be made upon these so-called "vegetating animals," and that at present it would be highly unsafe to consider them as symbiotic.
