44 PUIvSATlON OF JBLLYPISHES. 



the effects of magnesium. I find, indeed, that the center of the bell 

 of Gonionemus does occasionally pulsate spontaneously in sea-water, 

 and always pulsates actively whenever one touches it with a crystal of 

 KCl or K2SO4. It is not stimulated by the sea-water, but the inhib- 

 itory effect of the sea-water is probably due to magnesium, not to 

 potassium or calcium. The center of Gonionemus is strongly stimu- 

 lated by Na salts, and the reason it pulsates in ^n NaCl is that magne- 

 sium, as well as calcium and potassium, is withdrawn from the tissues 

 by osmosis by the pure NaCl solution, thus giving a preponderating 

 influence to the Na, which acts as a stimulant. Indeed, Loeb himself 

 found that the center of Gonionemus pulsates slowly in 96 c.c. Y^n NaCl 

 + 2 c.c. ^n KCl ■\- 2 c.c. "/ju CaClg. I also find that Gonionemus 

 pulsates slowly but without pauses in a solution resembling sea -water* 

 but lacking magnesium salts. The characteristic pauses which occur 

 periodically in the normal pulsation of Gonionemus are thus due to 

 magnesium. Magnesium fails to stimulate the center of Gonione- 

 mus, and, indeed, if the center be touched with MgSO^ or MgClj it 

 deadens the part touched, so that it responds weakly or not at all to 

 such powerful stimuli as the touch of a crystal of NaCl or KjSO^. 

 The disk of Cassiopea deprived of sense-organs behaves exactly as does 

 Gonionemus, for it does not pulsate spontaneously in sea-water but 

 does so in ^n NaCl, or in any solution containing NaCl -f K or Ca, 

 but lacking magnesium. If, however, we stimulate it with KCl or 

 K3SO4 it gives some active pulsations in sea-water ; or better still, if 

 we cut partial rings in its sub-umbrella and then stimulate it mechan- 

 ically by a shock, it pulsates indefinitely in sea-water. 



It is significant that the disks of Aurelia and Dadylometra, when 

 deprived of marginal sense-organs, still pulsate irregularly in sea- 

 water; and the disks of both of these Scyphomedusse sometimes 

 respond by weak contractions to MgSO^ and MgCl2.t They therefore 

 pulsate in sea-water as soon as they recover from the shock-effects 

 resulting from loss of their marginal sense-organs, because their 

 disks are stimulated by everything (Na, K, Mg) in the sea -water, 

 except the calcium, which, taken singly, exerts only a slight inhibitory 

 action. In the case of Cassiopea, Gonionemus, and Poly orchis the sea- 

 water is a balanced fluid. Na stimulates while Mg inhibits pulsation. 

 Ca in connection with Na and K is necessary to, and stimulates, 

 pulsation. 



* 96 c.c. H2O -f- 2.7 grams NaCl -\- 0.124 CaSOi -|- 0.01 CaCOs -|- 0.085 K2SO4. 



t These reactions are so irregular and the Medusas so extremely sensitive to mechan- 

 ical effects that I am in doubt concerning the validity of this statement. It may be 

 that the occasional response is due to some chemical shock-effect. 



