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



stimulated. In other words, the ganglion-cells of 

 this Medusa are able to originate two very different 

 kinds of impulse, according as they liberate their 

 energy spontaneously or in answer to direct stimu- 

 lation, and the muscular tissues respond with a 

 totally ditferent kind of contraction in the two 

 cases. Possibly, indeed, direct stimulation of the 

 ganglia is followed by a spasm of the muscular 

 tissue only because a greater amount of ordinary 

 ganglion intiuence is thus liberated than in the case 

 of a merely spontaneous discharge. If this were 

 the explanation, however, I should not expect so 

 great a contrast as there is between the facility 

 with which a spasm may be caused by stimulation 

 of the margin and of the contractile tissue respec- 

 tively. The slightest nip of the margin of Stauro- 

 phora laciniata, for instance, is sufficient to cause 

 a spasm, whereas even crushing the contractile 

 tissues with a large pair of dissecting-forceps Avill 

 probably fail to cause anything other than an 

 ordinary contraction. Nevertheless, pricking the 

 margin with a fine needle usually has the effect of 

 causing only a locomotor contraction. 



In conclusion, I may state that amesthetics have 

 the effect of blocking the spasmodic wave in any 

 portion of tissue that is submitted to their in- 

 fluence. It is always observable, however, that 

 this effect is not produced till after spontaneity has 

 been fully suspended, and even muscular irritability 

 destroyed as regards direct stimulation. Up to 

 this stage the certainty and vigour of the spasm 

 consequent on marginal irritation are not per- 



