6o Papers from the Marine Biological Laboratory at Tortugas. 



determined either from the one or the other, the living weight being prefer- 

 able on account of its greater magnitude and the consequent lessening 

 of the degree of error in its determination. Hence the reason for the 

 validity of the simple law that governs the loss of weight in the starving 

 jellyfish is that no appreciable chemical change occurs in the composition 

 of its body-substances, and there is no appreciable selective use of different 

 substances at different times during the progress of starvation. 



Sections show that as a physical result of starvation, the cells become 

 reduced in size, many degenerate and disappear, and the cell boundaries 

 tend to become indistinct; moreover, the gelatinous substance becomes 

 vacuolated and the muscular tonus is largely lost, so that the bell-rim bends 

 upward and inward in a balloon-like manner, as is shown in plate i, figure A, 

 which represents 6 medusae that have been starved 41 days and whose 

 combined weights have declined from 74.95 to 2.78 gm., all being still alive. 

 In fact, throughout these series of experiments no medusa has been lost 

 through natural death, although some of the series of observations upon 

 medusae starved in the dark were terminated on account of the develop- 

 ment of local maceration due possibly to ineffectually checked bacterial 

 activity. 



Plate I, figure B, gives an enlarged view of the smallest of these medusae 

 shown in plate i, figure A, and one may observe its crumpled, shrunken bell, 

 the loss through coalescence of the mouths, and the absorption of the 

 mouth-arm appendages. Indeed, the first organs to disappear are usually 

 the mouths and their appendages, and thus after being starved for about 

 3 weeks recovery may become impossible through the inability of the 

 animal to capture the zooplankton upon which the medusa feeds. Experi- 

 ments indicate that they do not feed upon diatoms, but in common with the 

 corals, as determined by Vaughan, their food appears to be exclusively of an 

 animal nature, the smaller forms of the zooplankton being taken into the 

 numerous mouths on the mouth-arms. 



It is known that much of the nannoplankton can pass through the best 

 filters, but one was unable to discover any specimens of the zooplankton 

 in the doubly filtered sea-water used in these experiments. Nevertheless, 

 medusae with their stomachs removed starve more rapidly than do animals 

 with their stomachs intact but regenerating their bell-rims. The medusae 

 which possess stomachs are, however, not called upon to regenerate any of 

 their parts and are thus subjected to less drain upon their resources. 



The value of a in the formula y = W{i — aY gives us a fair measure of 

 the rate of loss of weight. It may be called the "coefficient of negative 

 metabolism," for as a increases the loss of weight increases in like ratio. 



In the experiments recorded in this paper a ranges as shown in table 3. 



It appears from table 3 that Cassiopea thrives best and starves at its 

 slowest rate if maintained in large quantities of sea-water changed only 

 once in each 24 hours, thus resembling the conditions of the semistagnant 

 lagoons in which the medusa lives. 



