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 protoiilasm 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. \'er- 

 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 pi'otoplasmic extension of DitHiujcu 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 e.xcitation 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 centro.some or blejiharoplast from which strands radiate 

 to all the i^arts of the body which are concerned with locomotion, 

 l)ut 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, Steiitor, VorticeUa, 

 etc., have much more complicated reactions than Amoeba becau.se 

 of their more complex structures, but the stimuli to which they 

 resjiond are not much more complex or varied. The cilia are often 

 highly specialized and localized; some coordination must be neces- 

 sary. Cilia in general have been described in various ways as asso- 

 ciated with small granules at their ba.ses and strands from these 

 granules have been described as penetrating into the cells, in some 

 cases at least to be associated with a body of nuclear or cytoplasmic 

 origin. 



In 1880 Englemann found fibers in Stijlotu/chia to which he 

 assigned a nervous function. Nere.sheimer, 1903, found similar 

 fibers in Stoitar. and a number of others have described such 

 structures without always being clear as to their function. Sharp, 

 1913, considers an elaborate .system in Dijihulhiium which he calls 

 a "neuro-motor apparatus.' ' From a well-marked central body or 

 "motorium" strands of sub.stance 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 

 Ei( plates, developed from the ectoplasm. Fig. 1, C. It consists of 



