Medusae of the Philippines and of Torres Straits. 163 



say that if a sense-organ be cut off with only a small piece of tissue 

 around it the rate of pulsation will be much reduced. But young, 

 small jellyfishes pulsate more rapidly than large old ones, yet if we 

 graft two jellyfishes together the small active one will force the large 

 one to pulsate at its own rate, which will be even more rapid than the 

 normal rate of the small one, due to the large area of tissue the sense- 

 organs now control. 



Eimer and Romanes found that if the marginal sense-organs be 

 removed the jellyfish is paralyzed and responds only by single contrac- 

 tions to external stimuli. Later, in 1906, Mayer found that if the 

 sense-organs be removed and we cut a ring-shaped, or complete circuit 

 shaped, strip of tissue from the concave part of the bell, we may then 

 start a contraction wave proceeding in one direction through the circuit 

 through which it travels continuously, being indeed entrapped by the 

 circuit of tissue from which it can not escape. This movement is 

 almost machine-like in its regularity, and very different from the slow 

 and somewhat irregular pulsations the sense-organs engender. 



It is interesting to see that the pulsation stimulus in jellyfishes is 

 conducted by the nerves, whereas in the vertebrate heart it is conducted 

 by the muscles. There is, however, as Parker showed, a fundamental 

 likeness between nervous and muscular activity, for in most essential 

 features, such as the compensating pause following an extra pulsation 

 and the refractory stage during systole, latent period, reaction to tem- 

 perature, etc., the jellyfishes behave as does the vertebrate heart. In 

 Europe Romanes, Bethe, and von Uexkull, and in America Loeb and 

 Mayer have been most active in these studies. 



Recently Mayer finds that nerve conduction in Cassiopea is a chem- 

 ical reaction in which the cations of sodium, calcium, and potassium 

 take the active part, while magnesium is passive. The sodium calcium 

 and potassium appear to be attracted by adsorption to the surfaces of 

 some negatively charged colloidal elements of the nerve, and the veloc- 

 ity of nerve conduction is proportional to the degree of concentration 

 of these adsorbed cations. 



Thus if V be the velocity of nerve conduction, and C be the concen- 

 tration of the sodium calcium and potassium cations in the surrounding 

 sea-water, then for all dilutions down to sea-water mixed with an equal 

 volume of distilled water F=2.0 C' 86 where the velocity of nerve 

 conduction and the concentration of the cations in natural sea-water 

 are both 100. 



It is remarkable, as Goldfarb showed, that a jellyfish such as Cassi- 

 opea regenerates more rapidly in 90 per cent sea water (90 parts of sea- 

 water mixed with 10 parts of distilled water) than it does in normal 

 sea-water. 



In all scyphomedusse excepting the Rhizostomse tentacles are found 

 at the bell-margin, and usually grow out from between the notches of 



