224 Miscellaneous. 



ourselves of the action of light just indicated, to attract to the most 

 illuminated and most elevated i^oint in the vessel all the Planarians, 

 when we can convince ourselves that the fine bubbles of gas of 

 which Mr. Geddes speaks start from the particles of sand or the 

 organic fragments of the lower part of the vessel. On examining 

 with the lens the green mass formed by the Convolute^, we cannot 

 detect any gas-bubbles. Could it be otherwise with the continual 

 movement of the vibratile cilia, which is opposed to the formation 

 of the bubbles ? and in the absence of any internal cavity in which 

 the gases could accumulate or circulate ? 



The giving off of oxygen in the gaseous state would presuppose a 

 respiratory activity out of proportion to the small quantity of chloro- 

 phyll presented by our Planarians, even when collected into a great 

 mass. 



The bubbles obtained by Mr. Geddes presented from 43 to 52 per 

 cent, of oxygen, the rest being nitrogen. It seems to me that this resi- 

 due of nitrogen must not be neglected, and that it would be necessary 

 to assume that besides the 40 per cent, of oxygen, our worm excretes 

 60 per cent, of nitrogen of unexplained origin. It must further 

 be remarked that the analysis of the gases dissolved in sea-water 

 presents great difficulties and has not yet been made in a satisfactory 

 manner*. 



In reality, no completely aquatic plant or animal evolves gases 

 under normal and regular conditions, and the Convoluta forms no 

 exception to this law. 



In an excess of carbonic acid aquatic plants do not set free 

 oxygen except when they possess air-ducts and the leaves are de- 

 tached from the stalk, or when they have retained a layer of air 

 at the surface. In presence of an abnornal quantit)^ of carbonic 

 acid, the Convoliitee produce very small granules of amylaceous 

 matter which are deposited in the mesoderm. If the excess of 

 carbonic acid be too great the animals are destroyed ; then the asso- 

 ciation is broken up and the unicellular alga undergoes a new evolu- 

 tion, the course of which has still to be traced. 



Thus the respiratory act in Convoluta ScJmltzii consists in the 

 absorption through the cuticle of carbonic acid in solution, which 

 the chlorophyll decomposes with production of oxygen. The latter 

 is utilized by the animal in whole or in part, so that if oxygen is 

 exhaled it can be only in very small quantity and not in the gase- 

 ous state under normal conditions. This respiration presents a 

 striking analogy with that of submerged aquatic plants, such as we 

 must now-a-days conceive it to be. — Gom])tes Rendas, July 28, 1884, 

 p. 197. 



* See * Revue Scientifique,' June 21, 1884, and later. 



