Rhythmical Pulsation in Scyphomeduse. 121 
peeled away. Thus in figure 5, B, the area ruled with annular lines repre- 
sents a part of the ring from which the epithelial layer with its nervous 
network has been peeled away, leaving the muscles intact. Under these 
conditions the contraction is at once destroyed as soon as it reaches the 
border of the raw muscles and all movement ceases. 
If, on the other hand, we cut away both muscles and epithelium, and 
allow the cut area to regenerate, the nervous network and epithelium will 
regenerate before the muscles reappear. Thus in figure 5, 4, the dotted 
area represents a recently regenerated area, which contains no muscular 
elements, but over which the epithelium and nervous network has regene- 
rated. The contraction-stimulus passes readily through this region, although 
it can produce no contractions in the dotted area where there are no muscles 
to contract; all other parts of the circuit wherein the muscles are found 
contract as soon as the wave reaches them. Indeed, the pulsation-stimulus 
is independent of the muscles, and passes through the nervous network 
whether the muscles respond to it by contraction or remain inert. This 
is illustrated by figure 6, where the dotted sector ap represents newly re- 
generated epithelium, which contains the diffuse nervous network, but has 
no muscular elements and therefore can not contract. The undotted part 
of the sector ABC is normal tissue containing muscular elements, but it is 
immersed beneath a 54m MgSO, solution, which renders the muscles in- 
capable of contraction, although the pulsation-stimulus can still pass 
through the sector. The sector cp 
and the small undotted area around 
S is normal subumbrella tissue. If, 
now, a wave be started in this cir- 
cuit, it will pass constantly around 
the ring, and wherever it passes 
through the sector cp or over the 
area s these regions contract, for 
they are normal tissue, but no con- 
tractions or other visible signs of 
the presence of the stimulus are 
exhibited by the sectors which lack 
>==B 
Fic. 6.—Showing how a pulsation-wave may 
pass from normal tissue (plain area), 
muscular elements, or in which the 
muscles are rendered incapable of 
contraction through the effects of 
through tissue deprived of muscles (dotted 
area), and over muscles which have been 
rendered incapable of contracting through 
the effects of magnesium (immersed area). 
magnesium. 
But to return to our subject, if we cut a ring from the medusa’s disk 
such as is shown in figure 7 and leave a long narrow strip (AB) attached 
to it, and then start a contraction-wave traveling around the ring, every 
time the wave passes the point 4 a side-tracked portion of the wave will 
pass along the strip from A to B. When each side-tracked wave comes to 
