SYMBIOSIS AND "VEGETATING ANIMALS." 815 



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 algre ; and he records this remarkable experiment : " The expos- 

 ure 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, con- 

 taining on an average from thirty-two to thirty-eight per cent of oxy- 

 gen." He was able also to prove that this gas came from the associ- 

 ated alga? specimens destitute of alga? giving off no oxygen whatever. 



It is, therefore, now very certain that the yellow cells of radio- 

 larians and the pigment-bodies of coelenterates 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 coelen- 

 terates. 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 writ- 

 ten 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, be- 

 cause 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 de- 

 scribes 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. 



