Rhythmical Pulsation in Scyphomeduse. 123 
same rate as before. Robertson carried out his experiments upon the in- 
testine of a fly, and showed that if the intestine be placed in a decinormal 
solution of NaCl, peristaltic waves of contraction proceed down its entire 
length. If, now, any point near the middle of the length of the intestine 
be wetted with CaCl, or BaCl,, the wave of contraction is observed to 
completely disappear on entering this region, but on reaching the other end 
of the affected area the wave emerges with its initial rate and vigor. 
In Cassiopea the conductivity of the 
subumbrella tissue is independent of its 
contractibility. This is shown in figure 
8, where a series of radial cuts extend- 
ing part way in from the margin, or 
out from the center, oblige the pulsation- 
stimulus to travel inward and outward 
around the subumbrella. Then on stim- 
ulating the subumbrella by touching it 
with a crystal of KCl in each sector 
successively, the major wave is fully as 
likely to go inward toward the center of 
the subumbrella, where the tissue is rela- 
tively incapable of pulsating, as it is to Fic. 8.—Showing the observed direc- 
go outward toward the margin, where tions of pulsation-waves in a disk 
the muscles are well-developed and the deedeaagts AE AEPUE. BOIS. 10, see 
tissue contracts actively. Figure 8 rep- 
resents the conditions actually observed in a disk with 16 sectors. It will 
be seen that the major initial wave went inward in 7 of the tests, outward 
in 7 other experiments, and in both directions in the case of 2 trials. 
In so far as is known, all recurrently pul- 
sating animal tissues contain or are surrounded 
by the elements Na, Ca, K, and Mg. Marine 
animals at Tortugas, Florida, live in a solution 
which is well represented by Van’t Hoff’s 
solution 5m (100 NaCl + 7.8 MgCl, + 3.8 
MgSO, + 2.2 KCl + 3 CaCl,). On the other 
Mic. 9.—A pulsating ring of sub- hand, the pulsating organs of terrestrial or 
pee ee. ey) ae: fresh-water animals exist in the presence of 
the effects of a dissolved salt the same salts, but in amounts and proportions 
Baya she poleation: other than those of the above formula. 
We may readily test the influence of any solution upon pulsation in 
Cassiopea if we merely cut out a ring of subumbrella tissue, deprived of 
marginal sense-organs, set it into sustained rhythm, and then partially 
immerse the ring beneath the solution whose effects we wish to test (see 
figure 9). For example if the pulsating ring be partially immersed beneath 
