816 THE POPULAR SCIENCE MONTHLY. 



Professor Lankester's paper is full of entertaining facts of his own 

 discovery, but a number of experiments made by Mr. Blomfield, of 

 Oxford, and University College, London, and quoted by Professor Lan- 

 kester, are of special interest to us in this connection, as they furnish 

 some evidence that the green Hydra does, like Convoluta, evolve oxy- 

 gen in the sunlight. The observations are incomplete, but neverthe- 

 less of much value as they go to establish a second case in which 

 animals destitute of yellow cells and pigment-bodies, but endowed 

 presumably with true chlorophyl, do actually give off oxygen. 



Meantime the reader can not have failed to perceive that the ques- 

 tion as to the evolution of oxygen has become of secondary importance. 

 It is nothing strange if algas living in animals give off oxygen by virtue 

 of their chlorophyl. In any special case we must now first inquire 

 Are the colored parts mere plants dwelling within the animal, or are 

 they not ? If not, then we must, if possible, apply the spectroscope for 

 the study of the pigment (the chlorophyl group giving rather charac- 

 teristic spectra), and then, if chlorophyl is present, test, if we can, for 

 oxygen elimination. It is tolerably clear that the occurrence of native 

 chlorophyl in animal protoplasm is not so wide-spread as was suspected 

 before symbiosis was detected ; yet the cases of Hydra, Spongilla, and 

 Convoluta are still unsettled, and others may be added to their num- 

 ber : it must be granted, however, that the indications seem to be that 

 in some cases animals may possess veritable chlorophyl arranged as in 

 plants, giving the same spectrum and having the same power over car- 

 bonic acid. 



At present it will be far more profitable to consider the significance 

 of symbiosis than to speculate upon the result of observations belong- 

 ing to the future. Professor Semper, in his work entitled " Animal 

 Life," reminds us that, if it should come to pass [as it has] that we 

 must consider much of the chlorophyl found in animals to be borne 

 by vegetable messmates, we need not be surprised; since lichens 

 formerly supposed to be simple vegetables have now been shown to 

 be associated organisms a fungus parasitic uj)on algas. There is, in- 

 deed, much superficial resemblance between the two phenomena, and 

 it is said to have been from the literature of lichens that the expres- 

 sive word, symbiosis, was borrowed. In truth, there is really less 

 analogy than at first appears ; and, as there is no reason for consider- 

 ing the lichens as other than interesting and complicated cases of ])ara- 

 sitism, we may hereafter, I think, reserve the word symbiosis for the 

 description of that very different association of algse with animals 

 which it has been the purpose of the writer to elucidate. The word 

 zoophyte might, indeed, be used here with an accurate meaning had it 

 not already a very definite (though utterly senseless) use in pseudo- 

 scientific books and minds. 



Mr. Geddes pictures at considerable length the probable physio- 

 logical relationship between the organisms associated in symbiosis ; 



