142 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
sometimes so pronounced as to amount almost to 
a total destruction of contractional continuity 
between two or more quadrants of the bell; but 
more usually the effect of the marginal sections is 
merely that of destroying excitational continuity, 
or at least physiological harmony. 
It is an interesting thing that this form of section, 
although in actual amount so very slight, is attended 
with a much more pernicious influence on the 
vitality of the organism than is any amount of 
section of the general contractile tissues. Thus, if 
a specimen of Tiaropsis, for example, be chosen 
which is swimming about with the utmost vigour, 
and if four equidistant radial cuts only just long 
enough to sever the marginal canal be made, the 
animal will soon begin to show symptoms of enfeeble- 
ment, and within an hour or two after the operation 
will probably have ceased its swimming motions 
altogether. The animal, however, is not actually 
dead ; for if while lying motionless at the bottom of 
the vessel it be gently stimulated, it will respond 
with a spasm as usual, and perhaps immediately 
afterwards give a short and feeble bout of swimming 
movements. These surprisingly pernicious results 
are not so conspicuous in the case of Sarsia, although 
in this genus likewise they are sufficiently well 
marked to be unmistakable. I here append a table 
to show the comparative effects of the operation in 
question on different species. The cases may be 
regarded as very usual ones, though it often happens 
that a longer time after the operation must elapse 
before the enfeebling effects become so pronounced. 
