Rhythmical Pulsation in Scyphomedusce. 



129 



It is, then, evident that the relative powers of the inhibitors in sea- 

 water are from strongest to weakest magnesium, calcium, and potassium. 

 Indeed, the stimulating effect of the sodium chloride in the sea-water is 

 exactly offset by the subduing tendency of the magnesium, calcium, and 

 potassium ; and thus it is that the sea-water as a whole neither stimulates nor 

 inhibits the pulsation of the jelly-fish. The sea- water is, indeed, a delicately 



FIG. 12. Test of relative inhibiting power of magnesium, calcium, and 



potassium of sea-water. 



balanced fluid in all respects, for it contains poisons and antidotes which 

 exactly counteract one the other. 



The pulsation-stimulus is evidently not derived dircctlv from the sea- 

 water, but is engendered within the sense-organs of the bell-margin. 

 Experiments show that the sense-organs can not maintain pulsation unless 

 they be immersed in a fluid containing calcium in solution. Indeed they 

 must constantly be supplied with calcium. On the other hand the pulsation- 

 stimulus once it leaves the sense-organs and travels through the diffuse 

 nervous network of the subumbrella is relatively independent of the amount 

 of calcium in solution, for such a wave may endure for more than two hours 

 if traveling through subumbrella tissue, whereas the sense-organs can not 

 continue to send forth pulsation-stimuli for more than 6 to 10 minutes in a 

 solution which lacks calcium, but contains all the other elements of sea-water. 



We are now in a position to state that each pulsation is due to a nervous 

 stimulus that originates somehow in the sense-organs. The question is how 

 does it originate? 



In all of the Scyphomedusas the mar- f 



ginal sense-organs are little clubs, the 

 hollow entodermal cores of which con- 

 tain a terminal mass of concretionary 

 crystals. It has been commonly supposed 

 that these crystals are composed of cal- 

 cium carbonate, but I find that they are 

 actually calcium o.ralate with a certain 

 small proportion of urea and uric acid. 

 In nitric and hydrochloric acids they dis- 

 solve slowly without evolution of gas, but in sulphuric acid they slowly give 

 off bubbles of carbon dioxide. In short, they respond to all of the chemical 

 tests for oxalates. 



eel 



FIG. 13. Median section of marginal 

 sense-organ of Cassiopea xamachana. 

 ect., ectoderm; ent., entoderm ; oc., 

 ocellus; ot., concretionary crystals. 



