SYMBIOSIS AND "VEGETATING ANIMALS." 813 



in general be put (inferring from plants) is in decomposing carbonic 

 acid, and thus aiding alimentation, it has become an important ques- 

 tion to discover if this same physiological habit belongs to animal 

 chlorophyl. If it can be proved that animal substance endowed with 

 chlorophyl can, just as well as plant protoplasm similarly colored, 

 break down carbonic acid and utilize its elements, then we remove the 

 last formidable barrier between plant and animal protoplasm. If it 

 should be shown, on the other hand, that when found in animals it is 

 always functionally incapable of splitting up carbonic acid, it is true 

 that we preserve a point of difference between plants and animals, but 

 a result so negative would land us in a new difficulty, viz., that of ex- 

 plaining its presence by attributing to it some other function, and one 

 unknown to plant chlorophyl. No sufficient explanation of this kind 

 has hitherto been offered. In some cases a " protective resemblance " 

 to vegetation would explain its occurrence ; but in most cases this is 

 out of the question. 



Now, up to 1878 no evidence of value had ever been advanced to 

 show that animal chlorophyl does enable its host to split up carbonic 

 acid and give off the excess of oxygen resulting. In that year, how- 

 ever, Mr. Geddes, whose later work is referred to above, visited Ros- 

 coff and found there quantities of " the grass-green planarian (worm) 

 Convoluta Schultzii, of which multitudes are to be found in certain 

 localities on the coast, lying on the sand covered only by an inch or 

 two of water, and apparently basking in the sun. It was only neces- 

 sary to expose a quantity of these animals to direct sunlight to observe 

 the rapid evolution of bubbles of gas, which, when collected and ana- 

 lyzed, yielded from forty-five to fifty-five per cent of oxygen." 



Having obtained so much of valuable evidence, Mr. Geddes fol- 

 lowed up his discovery by examining these green worms to see wheth- 

 er or not the animal protoplasm derives the same kind of benefit from 

 its work as does plant protoplasm which is known, as a result of 

 the co-operation of chlorophyl, to build up starch or starchy com- 

 pounds. 



This, indeed, proved to be the case, for he adds : " Both chemical 

 and histological observations showed the abundant presence of starch 

 in the green cells ; and thus these planarians, and presumably also 

 Hydra, Spongilla, etc., were proved to be truly 'vegetating animals.' " 



The only link here needed is the full proof that the " grass-green 

 planarian " owed his color to veritable chlorophyl. There is little or 

 no reason to doubt it ; yet, when we are told by Professor Lankester 

 that in Spongilla alone among animals has spectroscopic investigation 

 really proved the presence of that pigment, we can not help wishing 

 that this confirmatory evidence had been obtained by Mr. Geddes. 



Meantime slow progress had been making in a kindred subject. 

 Before speaking of this, however, it must be said that chlorophyl is 

 now known to be by no means a simple substance, but is rather made 



