180 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



among the most persistent enemies of the fishes, for many an in- 

 cautious victim is ensnared among their deadly tentacles only to be 

 paralyzed and finally drawn upward into the mouth of the jellyfish. 

 It is, however, a poor rule which does not work in both directions, 

 and certain kinds of small fishes often accompany jelly fishes, swim- 

 ming in and out among the dangerous tentacles, even biting off small 

 pieces of the jellyfish itself and occasionally themselves falling a 

 prey to the stings, but in general enjoying a peculiar protection from 

 the attacks of larger fishes who dare not venture too near the jelly- 

 fish. 



The mouth, or mouths, of the jellyfish may be surrounded by veil- 

 like lips or, if the mouths are numerous, as in the so-called Rizo- 

 stomae (root-mouthed) jelly fishes, by complex frills lined by minute 

 tentacles which at intervals bend to and fro and sweep, as it were, 

 for food, for the jelly fishes are all carnivorous. In the higher 

 animals the intestine is a tube which lies suspended within the body 

 cavity, but Huxley showed that the jellyfishes have no body cavity, 

 and consist simply of a stomach and an outside with a mere 

 structureless lamella, or a solid mass of jell} 7 , between the stomach 

 wall and the outer skin layer of the animal. 



This gelatinous substance, which according to S. Hatai may be 

 allied in composition to chitin or cartilage, may serve as a store of 

 food for the animal in case of starvation, and Oassiopea can live at 

 least 42 days without food, the weight of the jellyfish declining 

 to less than one-hundredth of its original magnitude. The loss of 

 weight after the first day of starvation, and thus after all undigested 

 food has been discharged through the mouths of the jellyfish, follows 

 a simple law which shows that the loss of weight each day is propor- 

 tional to the weight of the animal at the beginning of that day and 

 thus the lighter it becomes the less weight lost. 



Thus, if W be the original weight of the jellyfish and y its weight 

 after x days of starving, then y=W {l—a) x \ where a is a constant, 

 less than unity. This shows that the source of energy during starva- 

 tion is chiefly the very large and simply organized gelatinous sub- 

 stance which, being very voluminous and heavy, is far more impor- 

 tant than the mere thin layer of cellular elements possessed by the 

 jellyfish. For, as is well known, vertebrates in starving first con- 

 sume glycogen, then mainly fats and lypoids, and finally proteid ele- 

 ments. Due, however, to the large volume of its gelatinous sub- 

 stance, the jellyfish chiefly consumes this during, starvation, although, 

 as Doctor Hatai showed, the starvation is in other respects simi- 

 lar to that of vertebrates. However, jellyfishes have on hand a con- 

 stantly ready source of sustenance, and can, so to speak, feed upon 

 their own bodies if deprived of prey. Mayer, 1914, carried out some 



