Converse Relation between Ciliary and N euro-Muscular Movements. 7 



pulsated the bell of the other must necessarily be mechanically drawn 

 together even though the pulsation-stimulus might not be able to pass 

 from one to the other. In order to obviate this possible ambiguity, two 

 individuals of Cassiopea xamachana were joined together so that their 

 subumbrella surfaces came in contact by a narrow isthmus, as shown 

 in fig. I. It was an easy matter to cause the medusas to unite in this 

 manner, but the union was usually of such a nature that no nervous 

 intercommunication was established and the two animals although 

 joined together continued to pulsate independently. In two instances, 

 however, a nervous union was established in from 5 to 7 days after the 

 operation, and then the individual which had the fastest rate of pulsa- 

 tion assumed control of the other, which always followed its every con- 

 traction. In both cases the small medusa, whose natural rate was the 

 more rapid, controlled the larger one, and caused it to follow its rate; 

 but if one pinched the bell-rim of the larger medusa its rate suddenly 

 increased so that it became faster than the small medusa, and then it 

 controlled the smaller until its excitement had subsided, when the smaller 

 one regained its control. This shows that the complex formed of the 

 two grafted individuals always pulsated at the rate of its faster mem- 



FlG. I. — Two individuals of Cassiopea xamachana grafted one upon another. 



ber. Prof. Jacques Loeb has called attention to the fact that in a coordi- 

 nated series of organs the whole series must beat at the rate of its fastest 

 component, and in this connection he cites the book-gills of Limulus, for 

 he finds that the whole series of gills moves at the rate of its fastest 

 member. Long before this Romanes demonstrated that Aurellia pulsates 

 at the rate of its fastest working sense-organ. 



I found that if the two medusae of the complex were cut apart by 

 severing the narrow isthmus of connecting tissue, the rate of each is 

 lower than that of the two when beating together. Thus in one case the 

 two medusae joined and beating in unison had a rate of from 31 to 34 

 pulsations per minute, but when cut apart one of the medusae had a rate 

 of 26 to 29 and the other 18 to 25 per minute. It is evident, therefore, 

 that the two medusae together behaved, in so far as pulsation is con- 

 cerned, as if they constituted a single individual, for Eimer and also 

 Romanes long ago demonstrated that small pieces cut from a pulsating 

 medusa beat slower than large ones. 



A certain nervous tonus is imparted to the sense-organs if they be in 

 nervous connection with a large area of subumbrella tissue. It is evident 

 that this tonus is not of a trophic nature, for the lowering of rate occurs 

 immediatelv when the medusae are severed one from another, and the 



