58 



Papers from the Marine Biological Laboratory at Tortugas. 



Table i. 



When the animal starves, this gelatinous substance decreases in volume and 

 apparently serves as the chief store of food for the starving animal. 



If W be the weight of the medusa when starving begins, aW may repre- 

 sent the decline in weight due to loss of body-substance and of water at 

 the end of the first day, so that at the end of the first day the weight of the 

 medusa is W — aW = W(i — a). 



Similarly, at the end of the second day the weight is W{i — a) — 

 aW{i - a) = Wii - ay. 



Hence the weight y after starving x days is 3' = W{i —a)' where a may 

 be called the index of catabolism, the rate of starvation increasing as a 

 increases. 



This formula accords fairly well with the facts of observation, as will be 

 apparent from an inspection of tables 4 to 27 and the curves accompanying 

 them. At times the observed weights are above and at other times below 

 the theoretical curve, but the general average in table i for 30 normal 

 medusae starved in the diffuse daylight of the laboratory is practically 



coincident with the curve 3' = W(i — 0.567)=^ for a 

 period of 19 days starving in filtered sea-water. 



Table i and figure i show the average decline in 

 weight deduced from six series of experiments upon 

 30 medusae of Cassiopea xamachana starved 19 days 

 in diffuse daylight in doubly filtered sea-water. 

 The weights are reduced to a scale of 100 grams 

 at the beginning of the experiment: Thus, if a 

 medusa weighed 10 grams at the beginning and 

 5 grams at the end of a certain number of days, 

 these weights would appear as 100 and as 50, re- 

 spectively, in the accompanying table : 

 This simple law governing the loss of weight in Cassiopea leads to the 

 conjecture that the chemical constitution of the animal does not change, 

 but that one and the same class of substances serves to maintain the medusa 

 throughout the period of its starvation. It is well known that in verte- 

 brates a very different condition pertains, for the starving animal at first 

 mainly consumes its store of glycogen, oxidizing it into carbohydrate; then 

 the fats are chiefly drawn upon, so that a starving vertebrate contains 

 relatively less fat and more proteid and water than a normal creature. 

 Thus there is a progressive change in the chemical constitution of the body 

 of the animal. 



This appears not to be the case in Cassiopea, and this supposition 

 receives further support from an analysis of the percentage of nitrogen in 

 the body, which appears to range from 2. 121 to 2.997 per cent of the dried 

 weight of the animal, the variation being independent of the number of 

 days the animal has starved. Hence it seems probable that starving 

 neither increases nor decreases the percentage of nitrogen. The results 

 are shown in table 2, wherein it appears that there is no coordination 



'Calculated according to the for- 

 mula y = 100(1 — 0.0567)*. 



