14 PUI^ATION OF JELLYFISHES. 



All experiments serve to demonstrate that the nervous relation- 

 ship between the sense-organs and the general sub-umbrella tissue is 

 reciprocal, as has been clearly shown by Romanes, who found that if 

 we cut a strip of tissue from the disk of Aurelia, leaving a sense-organ 

 at one end, and then gently stroke the end remote from the sense-organ 

 with a camel's hair brush, the marginal sense-organ at the other end 

 of the strip will be stimulated into sending a contraction wave back 

 over the strip (Romanes, 1885, pp. 74-77). This discharge is therefore 

 of a reflex nature. Nagel (1894) supports the idea that the marginal 

 sense-organs are reflex centers, while von Uexkiill (1901), upon evi- 

 dence which to me appears insufficient, concludes that the marginal 

 sense-organs in Rhizostoma pulmo are merely centers for the reception 

 of mechanical stimuli, and that each pulsation of the bell causes the 

 sense-organs to swing to and fro, and this stimulation calls forth a 

 new pulsation. 



We will show later that any point in the sub-umbrella surface may 

 be made to start and maintain impulses which will set the whole disk 

 into sustained and perfectly regular rhythmical pulsation. There is, 

 therefore, no difference of kind between the nervous activities of the 

 marginal sense-organs and those of any other parts of the sensory 

 surface of the sub-umbrella. 



As to the function of the otocysts in Hydromedusse, Murbach (1903) 

 showed that in Gonionemus they have no static function, for if they be 

 removed the normal movements of the Medusa will be resumed before 

 they are regenerated. Murbach 's conclusion that the seat of the static 

 function is "muscular sensation in the velum" requires confirmation. 

 Injury of so important a swimming organ as the velum may readily 

 cause irregularities in movements by abnormally deflecting the water 

 currents passing through the opening of the velum at each contrac- 

 tion. Moreover, Yerkes (1902), in his study of the sensory reactions 

 of Gonionemus, found that the velum is unaffected by stimuli of any 

 sort. 



Romanes (1885) found that the ocelli of Sarsia and Tiaropsis are 

 sensitive to light, and Yerkes (1902) demonstrated that the tentacles 

 of Gonionemus are very sensitive to chemical, mechanical, and photic 

 stimuli. 



The rates at which waves of contraction travel over the disk in 

 Cassiopea range from 150 to 1200 mm. per second, each individual 

 displaying a characteristic and constant rate. Apparently there is no 

 relationship between the size of the Medusa and the rate of trans- 

 mission of waves over its sub -umbrella tissue. These rates were 



