306 MENTAL FACULTIES SEC. 



mingled an element of consciousness. 1 This definition of the 

 term implies of course that he gives the name of instinct to 

 much which in my opinion is not instinct. For further 

 details I refer the reader to the book itself. 



IRRITABILITY AND SENSATION WILL 



In the preceding I have assumed that a brain is necessary 

 for the exercise of voluntary action, but it will be seen from 

 the following discussion, that I do not demand as the appar- 

 atus of voluntary action in multicellular animals a brain 

 morphologically recognisable as an organ, since in the lower 

 multicellular forms and in their larvae the ectodermic 

 or ectoblastic cells obviously are the instruments of voluntary 

 action. Of course beyond a certain stage of evolution certain 

 definite cells have more and more assumed the function of 

 central government. Where the seat of voluntary action is 

 to be sought in unicelullar forms, is a question which I shall 

 consider in the next section. Suffice it to say at present, that 

 it seems to me necessary even in these to assume a definite 

 organ in the cell as nerve-centre, which stores up the impressions 

 of the rest of the cell and makes use of them as if by will 

 that the whole cell-plasm together. cannot be brain. And 

 in like manner there must be paths in the cell which conduct 

 the external stimuli to the central organ. These paths are 

 probably protoplasmic threads, and on grounds to be subse- 

 quently set forth I believe I may claim the nucleus as the 

 central organ. For such nervous substance not yet morpho- 

 logically recognisable the term neuroplasm or nerve-plasma 

 may be used. But if voluntary action is to be assumed in 

 organisms which possess not even a nucleus, as in Monera, 



1 Op. cit. p. 169. Cf., on the other hand, Wundt, Grundziige der Psychophysik, 

 Leipzig, 1874, p. 809, et seq. ; this author advocates a view of instinct which in 

 essentials agrees with mine. 



