RESPIRATORY DIFFERENCES. 385 



duction tests, it is necessary to weigh the pieces in advance 

 since by this method only pieces of equal weight can be compared. 

 The sponges were cut into slightly unequal portions, and the 

 smaller portion weighed first. The larger portion was then 

 weighed and small pieces removed from it until its weight 

 equalled that of the other piece. After such handling it was 

 thought advisable to allow the pieces to stand in water for two 

 or three hour- before beginning the tests and this was always 

 done. 



Tin- -t.i-u.iirr used in all of the experiments was kindly 



furnished to me by Dr. A. J. Goldfarb. This water was collected 



t'n 'in iht cud of the Bureau of Fisheries pier at Woods Hole and 



stood for -cvcral flays prior to its utilization to allow debris to 



vet tic. This water contained no organisms visible to tin- eye 



but mi doubt some bacteria were present. As the blanks ln.\\- 



' lowed to stand as long as the experimental tubes before 



aiial\-is, this possible source of oxygen loss is cancelled out. 



I lie water was thoroughly aerated before use and was thus 



-aturated with air at the beginning of every experiment. 



In nearly all experiments two pieces of sponge were placed 

 in each tube, such pieces being of course from the same le\el 

 of the -ponies concerned. Thus for each experiment two spon 

 \\en elected and cut and the two apical halves placed in one 

 tube, tin two basal halves in the other. The tubes were then 

 tilled by siphon as already described. In some cases they were 

 tilled lirst and the pieces of sponges dropped in afterwards. In 

 the experiments on carbon dioxide production, the pieces were 

 placed in the tubes and with a pipette a definite amount of sea- 

 \\atcr colored with phenol red run into each tube. At first fivecc. 

 of uater \\ere added to each tube but the carbon dioxide pro- 

 duction \\as tCund to be so slow that later only two cc. were 

 employed. 



The control of temperature was difficult at Woods Hole. 

 < >\\ ing to the lack of constant temperature apparatus, the experi- 

 ments had to be run at room temperature. At the beginning of 

 en consumption experiment, the water and water bath 

 wen' allowed to come to room temperature and thereafter the 

 bath was kept at this temperature by adding warm or cold 

 water as the case might be. The carbon dioxide experiment-, 



