396 M. Reichert on the Morphology and Motory Phenomena 
e. During the contraction, the particles of the contractile 
substance must be displaced in a manner corresponding to the 
form of the state of action and of rest, and therefore according 
to a law. It must thus be conceived that the particles of the 
contractile substance during each state of action and of rest 
must have a determinate absolute and relative position cor- 
responding to the form in each case, that their displacement 
during the contraction is in this way regulated according 
to a law, and that the particles, after displacement, return to 
exactly the same absolute and relative position as that in which 
they were previously. Every other change in the absolute 
and relative position of the particles is excluded from the con- 
tractile action; hence the uniform mobility in every direction 
belonging to liquids is absent, as the absolute and relative posi- 
tion of the particles to each other in each case would depend on 
accidental external circumstances, and would comprise in itself 
the possibility of any changes in relative position. The con- 
traction of organized bodies is also distinguished from elasticity, 
quite independently of other phenomena, by the mobility of the 
particles only occurring in a definite direction, regulated with 
regard to the organized form. 
By comparison of the morphological properties and active motory 
phenomena of the two contractile structures, the following three 
differences become evident :— 
1. Muscular fibres are elongated contractile formations, in 
which the contractile particles are arranged with regard to a 
longitudinal axis during the state of rest. What the special 
form of the fibre may be, whether cylindrical or spindle-shaped, 
or flattened and terminating in a. lancet-shaped point, as 
the smooth unstriped muscular fibres, it may often be difficult 
to decide. But, for comparison, the fact is sufficient, that the 
contractile particles in a muscular fibre are arranged with regard 
to a longitudinal axis. 
Moreover muscular fibres exist as separate contractile ele- 
ments, by the aggregation of which the muscles and muscular 
lamine of the more highly developed animal organisms areformed. 
The contractile cortical layer of the Polythalamia forms 
during the state of rest a very thin membranous expanded con- 
tractile structure, in which the contractile particles are arranged 
with respect to a body expanded in breadth, or a disk. This 
layer, whether originating from cells or not, forms a continuous 
whole, in which no distinct contractile elements can be detected, 
with our present resources, in fully developed animals. 
2. In muscular fibres the property of contractility is, as far 
as our present observations extend, the principal, if not the only 
consideration to be taken into account, and to be estimated in 
