6 PULSATION OF JELLYFISHES. 



MINOR CONCLUSIONS. 



There are certain minor conclusions, mainly confirmations or am- 

 plifications of the excellent work of Romanes upon Scyphomedusse. 



In Cassiopea the sub-umbrella and mouth-arms are the only parts 

 which respond to mechanical or chemical stimuli. The ex-umbrella is 

 wholly insensitive. 



There is no essential difference in kind between the physiological 

 action of the sense-organs, in pulsation, and that of any other part of 

 the sub-umbrella. 



Cassiopea will live for more than a month in absolute darkness. 

 Its plant cells then degenerate, but the Medusa does not suffer; hence 

 its vitality is not dependent upon the commensal plant cells within 

 its tissues. 



Starved Medusse will shrink to about one-sixteenth their initial 

 volume and still survive. They will live in brackish water contain- 

 ing 75 per cent fresh water better than they will if we maintain the 

 amounts and proportions of calcium and potassium, merely reducing 

 the amounts of NaCl and magnesium of the sea -water. 



The fluids of the gastro-vascular space and of the body of the 

 Medusa are only slightly alkaline, while the sea- water at Tortugas 

 is decidedly alkaline. 



The sense-organs tend to send out contraction stimuli at various 

 rates, but the fastest working sense-organ controls the Medusa. 



Excitement of the disk forces the sense-organs to maintain a higher 

 rate of pulsation than they are capable of maintaining if cut off, 

 and it is evident, from other experiments, that the disk reacts recipro- 

 cally upon the sense-organs, stimulating them into activity. 



Small pieces of the disk, enervated by sense-organs, pulsate slower 

 than large ones. 



SmsdljyoUhg Medusae pulsate faster than large old ones. 



The sub-umbrella surface of the disk exercises a reflex control over 

 both sense-organs and mouth-arms. 



Repeated stimulation of any one part of the disk finally tires the 

 stimulated place so that it ceases to respond. Other parts of the disk 

 still respond as readily as did the tired place in the first instance. 



Having stated the principal conclusions, we will now proceed to 

 give a detailed account of the experiments upon Cassiopea, Lepas, 

 Salpa, and the loggerhead turtle. 



