208 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



of the facts cannot, I think, be disputed ; and it 

 fully explains why, in the unmutilated animal, the 

 degree of elongation on the part of the manubrium 

 usually exhibits an inverse proportion to the degree 

 of locomotor activity displayed by the bell. I may 

 here state that I have also observed indications of 

 muscular tonus in some of the other Medusae, but 

 for the sake of brevity I shall now restrict myself 

 to the consideration of this one case. 



To my mind, then, it is an interesting fact that 

 orano^lionic tissue, where it can first be shown to 

 occur in the animal kingdom, has for one of its 

 functions the maintenance of muscular tonus ; but 

 it is not on this account that I now wish to draw 

 prominent attention to the fact before us. Physio- 

 logists are almost unanimous in regarding muscular 

 tonus as a kind of gentle tetanus due to a persistent 

 ganglionic stimulation, and against this opinion it 

 seems impossible to urge any valid objection. But, 

 in accordance with the accepted theory of gan- 

 glionic action, physiologists further suppose that the 

 only reason why some muscles are thrown into a 

 state of tonus by ganglionic stimulation, while other 

 muscles are thrown into a state of rhythmic action 

 by the same means, is because the resistance to the 

 passage of the stimulation from the ganglion to 

 the muscle is less in the former than in the latter 

 case. Here, be it remembered, we are in the 

 domain of pure speculation : there is no experi- 

 mental evidence to show that such a state ot 

 differential resistance as the theory requires actu- 

 ally obtains. Hence we are quite at liberty to 



