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 tlie 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. 



