of the Contractile Substance of the Polythalamia. 357 
the structure as a whole. The contractile cortical layer of the 
Polythalamia is a principal constituent of the body as a whole, 
upon which its external form depends, and which exerts an 
action in regard to the entire body, not merely by its contrac- 
tility, but also by its respiratory secretory power, &c. 
3. The muscular fibre, on transition from a state of rest into 
the so-called active state or that of contraction, becomes changed 
into a flattened disk-shaped body. The contractile cortical 
layer of the Polythalamia, on transition into the active state, as 
is well known, appears in extraordinarily varying forms. When, 
however, it is considered that this contractile structure forms a 
continuous whole, in which the contraction ensues at any spot 
and to any extent, with the attraction of new contractile par- 
ticles, which augment the mass in action, alter the form, and, 
lastly, may increase to any extent, the distinctive and essen- 
tial relation on transition into the state of contraction may be 
characterized by the words “the contractile membranous plate 
finally changes into an elongate, under certain circumstances 
cylindrical body.” If the contractile energy is of but little in- 
tensity and is limited to a small spot, this form of contraction 
will appear as a small tubercle, and under the microscope as a 
minute granule upon the contractile membrane. If the tubercle 
enlarges, a more or less elongated papillary body becomes deve- 
loped from it, which appears as a tentacle or a pseudopodial 
process upon the contractile cortical layer continuous with it 
and in a state of rest. Lamellar processes and alveolar spaces 
will be formed by the contractile force of a segment of the con- 
tractile cortical layer corresponding to this form. Branched 
forms may be produced by increase of the contractile force in 
already existing processes, with attraction of new masses. A 
remarkable circumstance is, that the various forms resulting 
from contraction, as far as the present experiments extend, only 
occur upon the outer surface of the contractile layer. The cir- 
cumstances which are in action here are unknown; but the: law 
that the contractile cortical layer of the Polythalamia which in 
a state of rest forms a plate or disk, on passing into the active 
state finally assumes elongated variable forms, is not thereby 
altered. 
Of the three above-named differences, the first two, which 
refer to the purely morphological question, do not at present 
allow of further comparison. Both contractile structures are at 
all events morphologically of entirely different value and of 
different importance. The rational morphological relation of 
the two contractile structures to each other can only be deter- 
mined hereafter by an accurate knowledge of the history of the 
development of the body of the Polythalamia and of the mus- 
