On Changes in the Sea and Their Relation to Organisms. 



245 



lism of the muscle and other tissues was studied. The umbrellas of 3 

 cassiopeas, a, b, and c, of the same size ( diameter = 11.5 cm.) were used 

 (each for a series of experiments). In some experiments the rhopalia 

 remained and the normal pulsations were generated, in others a trapped 

 wave was induced, and in others the subumbrella was removed or 

 merely the mesogloea left. The apparent (but slight) metabolism of 

 the mesoglcea was probably entirely due to a few remnants of epithe- 

 lium and to bacteria, which always attack the mesogloea when the 

 epithelium is removed. At any rate, the metabolism of the meso- 

 glcea is too small to be of significance. The pH was 8.2 and the O z 

 per liter 4.5 c.c. at the beginning of each of the experiments. 



TABLE 20. 



The removal of the rhopalia in the umbrellas with trapped waves or 

 without pulsations reduced but slightly the amount of tissue. If we 

 take the metabolism of the normal pulsating umbrella at 100, the 

 exumbrella is about 14 and the resting subumbrella 60, with an addition 

 of 26 for normal pulsations or 65 for trapped wave. Therefore, the 

 neuro-muscular tissue may perform about 26 to 46 per cent of the 

 metabolism, and changes in rate or amplitude of the contraction-wave 

 are to be avoided as much as possible. 



In subsequent experiments, the manubrium and rhopalia were 

 removed from the cassiopea and a C-shaped cut was made through the 

 neuro-muscular layer, about one-third the radius from the outermargin 

 of the umbrella, and a trapped wave was induced by stimulation near 

 the outer margin. The wave passed around the outer part of the 

 subumbrella, and each time it passed the opening of the C it spread 

 to the inner part, dividing into two equal waves, meeting on the far 

 side with mutual destruction. In this way the outer part, in which the 

 trapped wave was first induced, was made pacemaker and the result 

 was a more permanent wave. The wave causes circulation of water 

 against all parts of the epithelium except a small portion of the exum- 

 brella which has a very low metabolism. If the oxygen concentration 

 was reduced to zero, the wave stopped and metabolism ceased until 



