304 THE PROTOZOA 



comparable to the differentiation of the diffuse ectodermal nervous 

 system of the Coelenterata, or to the ectodermal origin of the nervous 

 system in all higher Metazoa. 



Movement and reaction to stimuli have been the grounds usually 

 adopted in support of the view that Protozoa are endowed with intel- 

 ligence, and Eimer's view ('88) may be given as an example of this 

 type of reasoning. He says: "The ciliated Infusoria behave so in 

 regard to the outer world that one must ascribe to them the presence 

 of a will. The simple consideration of their movement from place to 

 place shows this. Change of position is entirely voluntary and is 

 effected through the greatest variety of motions ; sometimes all of the 

 cilia, sometimes this one or that one, move more slowly or more rapidly 

 or are kept quiet. The hypotrichously ciliated Infusoria, e.g. Euplotes 

 charon, sometimes paddle rapidly through the water by means of all 

 the cilia, sometimes run upon immersed objects, using their cilia 

 as legs, with a motion like that of an Asellus," etc. 1 If Eimer 

 could explain how he knows that such movement is voluntary 

 or involuntary, the conclusions concerning intelligence would have 

 some basis, but, as Haeckel says, the difference between voluntary and 

 involuntary movement is as difficult to define as it is to fix the boundary 

 between sensation (Empfindiing) and irritability {Rcizbarkeit), while 

 the latter shows no more trace of intelligence than do the very sensi- 

 tive reactions of Mimosas, DioiKza mustipula, and other higher plants. 

 If by voluntary action is understood a movement brought about by an 

 impulse or impulses, engendered more or less directly by external 

 stimuli, or by changes in the inner condition of the organism, then, 

 as Biitschli remarks, there is no reason for opposing the assumption ; 

 but if by voluntary action is meant that each stimulus or change in 

 outer conditions induces a response brought about by the intelligent 

 act of a will, then we are entirely without basis for the assumption of 

 such action in the Protozoa. 



While it is impossible to prove that movement is involuntary, 

 observations upon living organisms under different conditions, such, 

 for example, as the reactions of entire cells or the parts of cells to 

 artificial stimuli of various kinds, make it reasonably certain. 



Observations and experiments upon entire individuals are not con- 

 clusive, and the possibility of consciousness in perception and in 

 reaction is not excluded. It might indeed be argued that acids 

 " taste good " to Paramecium, or that antherozoids of the fern " like " 

 malic acid in small quantities as man likes alcohol, or that various 

 Protozoa " know enough " to turn away from harmful substances, 

 having acquired these characteristics through long ages of natural 

 selection. But similar responses to similar stimuli are shown by the 



1 Loc. cit., p. 340. 



