RHYTHMIC PULSATION 341 



and the various dilutions of sea water, namely that in the former 

 case the sphincters remained wide open, whereas in the latter 

 instances the sphincters (as in 'normar exhaustion in 100 per 

 cent sea water) were more or less contracted, though with the 

 rain-water effect it was not a matter of the contraction of the 

 anal dilators, but rather of the more complete relaxation of the 

 circular constrictors. 



With rain water it was found that the brownish skin pigment 

 rapidly made its appearance in the water surrounding a beating 

 cloacal end even before pulsation ceased. This effect became 

 apparent after immersion of about 5 minutes. It was, under 

 certain circumstances, found with other concentrations of sea 

 water, but (as will be shown subsequently) it could be inhibited 

 by the presence of non-electrolytes. This reaction may indicate 

 either that the permeability of the superficial cells had been very 

 Ifighly modified, or that the cells surrendering their coloring 

 matter were dead; inasmuch as the pigment loss did not occur 

 more at the region of the cut end of the pieces than at any other 

 place, and could be inhibited by the addition of sea water, and 

 further inasmuch as the region of the cut end did not give off any 

 visible amount of pigment into normal sea water, it might rea- 

 sonably be held that the latter alternative is not necessarily the 

 correct one. It is possible that at concentrations much removed 

 from that of normal sea water the cells of Stichopus became 

 rather highly permeable for salts while still alive. This possi- 

 bility was suggested by the very evident amounts of chlorine 

 found in rain water in which pulsating pieces had lain. If this 

 permeability for salts could be proved over the lower range of 

 concentrations here dealt with, the form of the lower parts of 

 the curves in figure 29 might readily be accounted for; between 

 per cent and 95 per cent these graphs might result if the critical 

 internal conditions (salt concentrations?), beyond which no 

 spontaneous pulsation is possible and irritability ceases, were 

 approached (1) by the intake of water and at the same time (2) 

 by the exit of salts. 



It is stated by Mayer ('14 ^- p. 40) that the rate of nerve con- 

 duction in operated Cassiopea is accelerated by slight dilution 



