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 different 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 influence 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 will 
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 anzesthetics 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- 
