8 NERVOUS SYSTEM AND SENSE ORGANS 
sess are not capable of demonstration or proof. All that we can see 
is that if there are any elements of consciousness they must be of a 
very vague and elementary nature. 
All forms of protoplasm have the property of irritability and 
there is usually also involved a certain degree of conductivity, but 
these are not always possible to measure or clearly determine. Ver- 
worn has made a study of conductivity in the elongated thread-like 
pseudopodia of some rhizopods. In studying the changes which 
take place in the long protoplasmic extension of Difflugea the re- 
sults of stimulation may be directly observed. A weak stimulation 
at the end of the pseudopodium causes a slight wrinkling of the 
smooth surface, a stronger stimulus causes more swellings and more 
distant ones on the slender appendages. Fig. 1, A, B. The extent 
and rapidity of the wrinkling of the surface is in direct response to 
the strength of the stimulus applied. Other species of rhizopods 
gave similar results. The decrement of the intensity and rapidity 
becomes greater with the distance from the point of stimulation 
until the wave of excitation is obliterated. This is of course in 
sharp contrast to the conduction of a nerve fiber which normally 
conducts excitations without perceptible decrement of the intensity. 
An organ for the control of amoeboid movement has been sug- 
gested, a centrosome or blepharoplast from which strands radiate 
to all the parts of the body which are concerned with locomotion, 
but no recent proof of this suggestion has come to my attention. 
According to Hyman the nucleus in Amoeba plays an important 
part in amoeboid movement, as is shown when the nucleus is re- 
moved. 
Ciliate Protozoa such as Paramoecium, Stentor, Vorticella, 
etc., have much more complicated reactions than Amoeba because 
of their more complex structures, but the stimuli to which they 
respond are not much more complex or varied. The cilia are often 
highly specialized and localized; some codrdination must be neces- 
sary. Cilia in general have been described in various ways as asso- 
ciated with small granules at their bases and strands from these 
granules have been described as penetrating into the cells, in some 
eases at least to be associated with a body of nuclear or cytoplasmic 
origin. 
In 1880 Englemann found fibers in Stylonychia to which he 
assigned a nervous function. Neresheimer, 1903, found similar 
fibers in Stentor, and a number of others have described such 
structures without always being clear as to their function. Sharp, 
1913, considers an elaborate system in Diplodiniuwm which he calls 
a “neuro-motor apparatus.’ ’ From a well-marked central body or 
“motorium” strands of substance were found going to the cilia 
and to various parts of the body in a complex manner. Fig. 1, F, 
G, H. Yocum, 1918, describes and figures a neuromotor system in 
Euplotes, developed from the ectoplasm. Fig. 1, C. It consists of 
