6 



Papers from the Department of Marine Biology. 



from 17.5 to about 36 or 38 when it suddenly declines, the fall in 

 rate indicating injurious effects, possibly due, as Harvey suggests, to 

 the destruction of an accelerating enzyme. For several degrees, 

 both above and below 29, the rate changes about 4.5 per cent for 

 each 1 C., and this correction was applied to all records. The records 

 in diluted sea-water were usually taken at higher temperatures than 

 those in the pure sea-water with which they were compared. The 

 greatest average range was, however, not more than 1.79 C., but all 

 records were reduced to the rate they would have exhibited had they 

 been taken in a solution at the same temperature as that of the pure 

 sea-water with which they were compared. 



Another correction must be made on account of the osmotic inter- 

 change between the tissues of the ring and the diluted sea-water in 

 which it is placed. Each experiment was made after the ring had been 

 for one hour in 500 c.c. of fluid and a series of titrations with n/10 

 AgNOa, using K 2 Cr0 4 as an indicator, showed the osmotic interchange 

 had augmented the concentration of the diluted sea-water as follows: 



TABLE 1. 



The subumbrella tissue of Cassiopea xamachana is infested with 

 commensal plant cells and thus when pulsating in diffuse daylight 

 it gives out very little free CO 2 . If placed in the dark, however, the 

 sea-water surrounding the medusa soon becomes acid, due to the 

 unreduced CO 2 . All experiments were conducted during daylight hours 

 in the diffuse light of the laboratory, and a series of tests showed that 

 there was no appreciable change in the hydrogen-ion concentration of 

 the pure or of the diluted sea-water after the pulsating ring had been in 

 500 c.c. of the solution for 1 hour. The laboratory was provided with a 

 Leeds and Northrup potentiometer, which had been standardized by 

 the U. S. Bureau of Standards; also with a Bovie potentiometer and 

 two sets of standardized colorometric tubes made by Hynson, Westcott, 

 and Dunning, one set being that of Rowntree, Levy, and Marriott, and 

 filled with phenolsulphonephthalein, and the other set that of McClen- 

 don, wherein the tubes are filled with graded solutions of thymolsul- 

 phonephthalein. Both these sets of tubes were standardized by Pro- 



