62 Papers from the Marine Biological Laboratory at Tortugas. 



Bearing this in mind, the sea-water was doubly filtered and then heated 

 to 71° C. after which it was allowed to cool in sterilized glass vessels pro- 

 tected from dust. Medusae kept in this sterilized water, whether in the 

 dark or in daylight, lost weight no more rapidly than would have been the 

 case had they been starved in sea-water that had been merely passed through 

 four Chardin filter papers without being sterilized by heating. 



When sea-water is heated to 71° C, however, some of its dissolved air is 

 expelled, and in order fully to compensate for this medusae were starved in 

 a control sea-water solution which had been placed in a vacuum under the 

 receiver of an air pump, thus expelling far more air than was lost by the 

 sea-water which had been heated to 71° C. It was found, however, that the 

 commensal plant-cells of the medusa render the animal comparatively 

 independent of the oxygen of the sea-water, provided an excess of CO2 be 

 absent, and thus the medusa starves at practically the same rate in heat- 

 sterilized, air-exhausted, or normal filtered sea-water. In fact, it starves 

 at this same rate in sea-water which has been doubly filtered through the 

 Chardin filters and then refiltered through porcelain to extract bacteria 

 and nannoplankton. Putter's^ "dissolved food" of sea-water may, there- 

 fore, still be available as food even after all organisms have been taken 

 out of the sea-water, and it appears that such organisms are not necessary 

 to initiate a process of assimilation. 



If the stomach be intact, the animals starve less rapidly than if it be 

 removed. Animals whose stomachs have been cut off can regenerate new 

 gastro-vascular centers, but this is rarely done, and it so happened that none 

 of the disks studied by me succeeded in replacing their stomachs, although 

 all made more or less progress in regeneration. 



In order to determine the effect of the regeneration, we compared the 

 starving rate of these agastric medusae with others having stomachs intact 

 but regenerating their bell-rims, an annulus of the bell being cut off close 

 to the outer edge of the stomach, as is shown in plate i, figure C. 



Table 3 and tables 18 to 25 show that disks without stomachs lose 

 weight about 1.25 times as rapidly as do regenerating medusae with stomachs 

 intact. 



Carbon dioxide plays a conspicuous r61e in controlling the activities 

 of the medusa, for Harvey^ found that during the day the velocity of nerve- 

 conduction is greater than during the night, and this fact is possibly due 

 to the variation in the supply of oxygen conditioned by symbiotic algae 

 in the subumbrella tissue of the medusa. 



It was found that if we make a weak solution of rosolic acid in sea-water 

 and divide it into two equal volumes in two separate containers and then 

 cut a medusa into halves and place each half in a volume of the rosolic-acid 

 solution, it will be observed that if one half of the medusa be kept in diffuse 

 daylight and the other half in darkness, the rosolic acid surrounding the 



'The most complete presentation of Putter's views is given in his recent worlc "Die Emahrung der 

 Wasserthiere und der Stoffansalt der gewasser" (Jena, igio). 



' Harvey, E. Newton. Carnegie Institution of Washington, Year Book No. lo, ipHi p. I3i. 



