882.] Zoology. 743 



Concluding Observations on th 



Medus/e. — Mr. G. J. Romanes has, by his experiments upon Me- 

 dusae, done much to explain the nature and origin of nerve action. 

 It is in the Medusae that we have the first observed appearance, in 

 the ascending scale of life, of both muscular and nervous ele- 



der experimentation, and are, many of them, of considerable size. 

 A startling result of Mr. Romanes' labors, is his conclusion that 

 ganglionic action is not, by itself, adequate to explain rhythm. 

 Rhythmic action is the rule in the lowest forms of animal life ; the 

 beautifully regular motions of some Algae, Diatoms and Oscillato- 

 riae, of the Infusoria, etc., are certainly not due to ganglia — not 

 the least vestige of a ganglion can be traced in the snail's heart; 

 and it would be hard to decide in what respect the beating of the 

 snail's heart differs, on the one hand, from that of the pulsatile 

 vessels of the Infusoria, or, on the other, from that of the mam- 

 malian heart. This being the case, why, Mr. Romanes asks, 

 should the rhythmic action of the latter be referred to the ganglia 

 present in it? Does it not seem probable that those contractile 

 tissues endowed with rhythmic action in the higher animals 

 are those which have retained their primitive endowment of 

 rhythmicality ? The paralyzed nectocalyces of Medusae yield a 

 rhythmic response to stimulation, whether electrical, mechanical 

 or chemical, 'but while the covered-eyed Medusae respond most 

 readily to faradaic stimulation, some of the naked-eyed Medusae 

 are acted on most powerfully by the constant current, as well as 

 by mechanical and chemical stimulation. The effect of tempera- 

 ture upon the rate of contraction exhibited by tissues deprived 

 of their ganglia (artificial rhythm) was exactly parallel with its 

 effect upon the natural rhythm of the motions of the unmutilated 

 tissues, and this leads up to the probability that the effects of 

 temperature on the natural rhythm of the ganglio-muscular tis- 

 sues of other animals are for the most part exerted on the con- 

 tractile element instead of on the ganglionic. 



The introduction of oxygen gas into the water containing the 

 parts under the action of electrical stimulus, increased the rate of 

 contraction, while carbonic acid gas diminished it. The removal 

 of the periphery of the swimming- bell of Sarsia, with its accom- 

 panying ganglia, causes great elongation of the polypite. The 

 same thing occurs in some other Medusae, but to a less extent. 

 Thus the polypite is normally in a state of tonic muscular con- 

 traction from the persistent ganglionic stimulation, while the bell, 

 under the same stimulation/exhibits rhythmic action. This dif- 

 ference is believed to result from the greater irritability of th..- p< Ax 

 Pite. which is evident in whatever way a stimulus is applied. But 



movements of the healthy animal, Mr. Ro- 

 manes conclude, that the ganghom, d^eharge, are timed to co- 

 incide with the rhythmic action of the contractile tissues, due to 



