214 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
agent is much the same as that of chloroform—the 
description just given being quite as applicable to 
the effects of the nitrite as to those of chloroform. 
Before the loss of spontaneity supervenes, the rate 
of the rhythm is increased, while the strength of 
the pulsations is diminished. 
Tiaropsis diademata, from the fact of its present- 
ing a very regular rhythm and being but of small 
size, is a particularly suitable species upon which 
to conduct many experiments relating to the effect 
of poisons. On this species the nitrite in appro- 
priate (7.e. in very small) doses first causes irregularity 
and enfeeblement of the contractions, together with 
quickening of the rhythm. After a short time, 
a gradual cessation of the swimming motions be- 
comes apparent—these motions dying out more 
gradually, for example, than they do under the 
influence of chloroform. Eventualiy each pulsation 
is marked only by a slight contraction of the 
muscular tissue in the immediate neighbourhood of 
themargin. If the dose has been stronger, however, 
well-marked spasmodic contractions come on and 
obliterate such gradual working of the poison. In 
all cases irritability of all parts of the animal 
persists for a long time after entire cessation of 
spontaneous movements—perhaps for three or four 
minutes in not over-poisoned animals ; but eventu- 
ally it too disappears. On being now transferred 
to normal sea-water, the process of recovery is 
slower than it is after aneesthesiation by chloroform. 
It is interesting, moreover, to observe, that just as 
the power of co-ordination was the first thing to be 
