188 J'UIHTX from th<- Department of Marine Biology. 



the period between experiments, as these organisms quickly become 

 abnormal if allowed to lie prone on their side on the bottom (Cary, 

 1914, p. 86). The specimens were kept in a live-car in the intervals 

 between the experiments, so that their condition was normal, as was 

 shown by the fact that the colonies would remain in good condition in 

 this live-car for at least two months. 



The sea-water for each series of experiments was brought fresh from 

 the ocean in large aquarium jars and the respiration chambers were 

 filled by submerging them in the large jars. The temperature was 

 controlled by placing the respiration chambers in an aquarium contain- 

 ing about 75 liters of sea-water. This aquarium was covered with a 

 black box to exclude the light, as some of the species studied con- 

 tained within their tissues enough symbiotic algae (Zooxanthellre) to 

 materially influence the results when the experiments were carried 

 on in the diffuse light of the laboratory. This thermostat was con- 

 nected with the running-water supply of the laboratory and during a 

 2-hour experiment (the usual duration) the temperature would not vary 

 more than 0.2 C. On unusually hot days, when the temperature of 

 the ocean-water over the shallow reef flats was subject to marked fluc- 

 tuations, it was found that a much more even as well as lower temper- 

 ature was obtained by cutting off the water-supply to the tank, as the 

 early morning temperature of the water would then be maintained 

 within half a degree throughout the day, while the variation during the 

 time of a single experiment would not be measurable with a thermom- 

 eter reading to 0.2 C. 



The oxygen in the water was determined by the Winkler method, 

 using the precautions as regards the purity of reagents described by 

 McClendon (19176). Before taking the sample for analysis at the 

 end of an experiment the respiration chamber was inverted several 

 times to insure complete mixing of its contents. An extended series of 

 comparisons showed that there was no detectable difference in the 

 results obtained by drawing the water sample 250 c.c. through a 

 glass siphon into the empty bottle or when siphoning into a bottle 

 by the displacement of mercury (McClendon, /. c.). The former, 

 less complicated and much more rapid, method was therefore followed. 

 The hydrogen-ion concentration (P H ) of each fresh supply of water was 

 determined by a colorimetric method and the amount of C0 2 which it 

 contained calculated from the P H and reserve alkali by a conversion 

 table (McClendon, 1917). In all the experiments it was found that 

 so great a quantity of acid other than CO 2 was being given off that the 

 values obtained for a respiratory quotient were far higher than would be 

 obtained from the combustion of pure carbohydrates. Since the respir- 

 atory quotients were in every instance greater than unity, whatever 

 the duration of the experiment, they have not been included in the table. 



