44 PULSATION OF JEUvYFlSHES. 



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 

 KC1 or K 2 SO 4 . 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 sium , as well as calcium and potassium, is withdrawn from the tissues 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, L,oeb himself 

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

 + 2 c.c. ^n KC1 + 2 c.c. 10 / 8 n CaCl 2 . 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 4 or MgCl 2 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 K 2 SO 4 . 

 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 + K or Ca, 

 but lacking magnesium. If, however, we stimulate it with KC1 or 

 K 2 SO 4 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 Dactylometra, when 

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

 water; and the disks of both of these Scyphomedusae sometimes 

 respond by weak contractions to MgSO 4 and MgCl 2 .f 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. H 8 O 4- 2.7 grams NaCl + 0.124 CaSO 4 + 0.01 CaCO 3 + 0.085 K 2 SOi. 



f These reactions are so irregular and the Medusae 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. 



