DEPARTMENT OF MARINE BIOLOGY. 219 



From the quantitative determinations of CO2 production under various con- 

 ditions, the following conclusions are reached: 



1. An annular piece cut from the peripheral region of the body produces an 

 exceedingly small amount of CO2. This low production of CO2 does not, 

 however, indicate a low rate of metabolism in Cassiopea, for, if the estimation 

 is made in darkness, CO2 production is more than doubled. This result 

 confirms the fact observed by Mayer, and familiar to all who work "svith this 

 form at Tortugas, namely, that commensal plant cells, within the gelatinous 

 substance of the disk of the animal, synthesize the CO2 in light. 



2. CO2 production in Cassiopea, measured even in darkness, is much less 

 than in any other tissues I have as yet studied, with the probable exception 

 of unfertilized eggs of Fundulus heteroclitus. This, however, is due to the 

 large proportion of comparatively inactive gelatinous substance in the exum- 

 brella region, which gives less than one-fourth the CO2 given off by the sub- 

 umbrella regions. Mayer has shown that the subumbrella region is a most 

 active portion, physiologically, and is exceedingly sensitive to CO2, while the 

 animal can go on functioning even if the exumbrella region is killed by HgCl2. 

 My results seem to indicate that the more metabolically active the tissue the 

 more susceptible it is to stimuh. 



3. Mayer found that rate of nerve conduction in the subumbrella region 

 increases about 5 per cent in sea-water diluted with distilled water (9 : 1), 

 while it decreases to about 50 per cent in 50 per cent sea-water. By using 

 0.9 molecular dextrose instead of distilled water, he obtained practically the same 

 effects. By these experiments he demonstrated that the decrease in the rate 

 of nerve impulse in sea-water diluted with distilled water is not due to the 

 decrease in osmotic pressure, but to the corresponding change in the concentra- 

 tion of the electrolytes. I have previously endeavored to show that changes 

 in physiological activities produced by change in concentration of the elec- 

 trolytes is very closely associated with changes in tissue metabolism. The 

 change in the rate of nerve impulse in Cassiopea, therefore, may be directly 

 correlated with the change in the metabolic activity which might take place in 

 the nerve tissue. My experiments show that a corresponding change occurs 

 in the CO2 production in the subumbrella region if the animals are treated as 

 was done by Mayer. The decrease of CO2 production in a diluted sea-water 

 is more decidedly shown if we take the regenerating ectoderm before the 

 muscle regenerates. These results strongly suggest that the decrease of 

 metabolism in the nerve tissue may be the primary cause of the decline of 

 rate of nerve impulse in Cassiopea in dilute sea-water. 



4. At the request of Dr. Gary, the follo^ving observations were made : 



(a) A semi-annulus cut from the peripheral portion of one half of the disk 

 of Cassiopea without sense-organs gives off less CO2 than one cut from the 

 corresponding half with sense-organs intact. Neither piece contracted during 

 the experiments. 



(6) A semi-annulus cut from the peripheral portion of a half disk of Cassiopea 

 with sense-organs intact gives more CO2 than one cut from the corresponding 

 half of the animal without sense-organs, but which had been stimulated elec- 

 trically so as to produce contractions before the time of the experiment, 

 although both halves were quiescent during the experiment. 



5. Does sea-w^ater contain free CO2 ? 



This question was considered upon a request of Doctors Mayer and Vaughan. 

 Working upon samples of Tortugas sea-w^ater collected by Dr. Vaughan, Mr. 

 Dole came to the following conclusion: "The quantities of acid required to 

 neutralize the cold sea-water in presence of phenolphthalein proves conclu- 

 sively that free carbon dioxide, in the ordinary acceptance of the term in 

 America, is not present." I have undertaken to conduct a similar investi- 



