Rhythmical Pulsation in Scyphomeduscs. 



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 2 , 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. 



c> 



In Cassiopca 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 KC1 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 

 go outward toward the margin, where 

 the muscles are well-developed and the 

 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 Torttigas, Florida, live in a solution 

 which is well represented by Van't Hoff's 

 solution ^m (100 NaCl -f 7.8 MgCL + 3.8 

 AlgSO, + 2.2 KC1 -f 3 CaCL ) . On the other 

 hand, the pulsating organs of terrestrial or 

 fresh-water animals exist in the presence of 

 the same salts, but in amounts and proportions 

 other than those of the above formula. 



FIG. 8. Showing the observed direc- 

 tions of pulsation-waves in a disk 

 stimulated at various points in suc- 

 cession. 



FIG. 9. A pulsating ring of sub- 

 umbrella tissue partially im- 

 mersed in order to determine 

 the effects of a dissolved salt 

 upon the pulsation. 



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 



