Igo Herbert W. Rand 
The closing of the cut end of a stem of Tubularia, as described 
by Morgan (’o1), is in some respects as simple a case as may be 
found. The cut end of a stem is closed in less than half an hour 
by means of a concentric centripetal extension of the old cceno- 
sarc. This extension forms a thin plate transverse, or nearly so, 
to the axis of the stem. “This plate is composed of two layers of 
cells, of which there are a number of rows arranged concentrically 
between the center and the outer edge” (p. 69). It is to be in- 
ferred from the account that the two layers of cells represent the 
ectoderm and the entoderm. ‘The final closing takes place at the 
center of this plate. The manner of formation of the plate, and 
the fact that the closing is complete are inconsistent with the idea 
that the process is one which depends upon the contraction of 
muscle fibers. Moreover, there are supposed to be no muscle 
fibers in the stem of Tubularia. Morgan’s conclusion, that the 
closing is effected by activities of the ccenosarc cells akin to, if not 
identical with, amoeboid motion, seems to be the most plausible 
view of the matter. 
Experiments upon Hydra viridis afford similar phenomena. 
When the column is cut transversely the cut edges of the body 
wall slowly bend inward and within an hour the cut end is com- 
pletely closed. The closed end is somewhat convex in formand 
both of the body layers are there present. It is perhaps possible 
that the closure in this case is accomplished by means of the mus- 
cle cells. Yet there is good ground for believing that activities of 
other kinds participate in the closing process even if they are not 
accountable for the whole of it. After the transection the cut 
edges at once bend inward slightly. This immediate change may 
possibly be due to contraction of the muscle processes. Again, 
if a column of Hydra is split lengthwise, each half column at once 
shows a tendency to roll into a cylinder with the ectoderm upon the 
outside, while at the same time it curls lengthwise into a flat spiral 
with the cut edges on the inside of the curve (Rand ’99). This 
behavior, also, may result from muscular contraction. It should 
be noted, however, that the entoderm layer is much thicker than 
the ectoderm, and therefore the layer of muscle processes is not 
equidistant from the inner and outer surfaces of the body wall, but 
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