188 3] Organic Physics. 143 
Sensitiveness seems confined to special protrusions of the proto- 
plasmic mass, while the remaining surface has lost its irritability. 
Possibly it has become sheathed in insensitive substance. Cilia 
are perhaps composed of naked protoplasm, and adapted to per- 
form at once nervous and muscular duties. They may represent 
in the Protozoa the separate nerves and muscles of the Metazoa ; 
and may also represent, in ciliated epithelial cells, the individual 
life function of all cells. Everywhere that cells are exposed to 
external contact they display receptive adaptations ; but fail to do 
so when shielded from contact. The cilia must constantly feel 
the fine currents which can scarcely ever be absent from liquids. 
Thrills of vibration may thence be sent down into the protoplas- 
mic mass, and oxidation induced. The energy arising may be 
reflected back into the cilia, as the most motile portions of the 
mass, As for their specially directed motions it is quite possible 
that they may be specially related to the mass, and free to move 
only in certain directions. 
If the motor and sensory functions of single-celled animals are 
thus confined to minute filaments, the similar functions in the 
many-celled animals are likewise confined to cellular filaments or 
fibers, arranged to conduct vibratory energy in certain directions, 
and to yield motion to certain limbs and organs. The bodies ot 
the higher animals are permeated by lines of conductive material, 
Insulated from the surrounding tissue, and with their surface ex- 
tremities consisting of naked protoplasm. These conducting 
lines Jead to peculiarly arranged masses of fibers, into which are 
discharged the vibratory influences which they carry inward. 
Motor changes take place in these muscular fibers in response, 
and these changes are always accompanied by oxidation. Quite 
possibly the motor impulse which the nerve has received from 
external contact or pressure, is carried inward and delivered to 
the muscle as a vibratory energy, which induces chemical com- 
bination between the commingled oxygen and protoplasm mole- 
cules. : 
All the motor functions of the highest animals are unquestion- 
ably results of the physical character of protoplasm, and of its 
Special arrangements. The principles of motor activity which 
= find in the Rhizopod exist in the man, and no others. Proto-. 
plasm, wherever found, is subject to fapid oxidation when exter- 
* motor influence sends a vibratory thrill through it. This 
