1889 - 90 .] 
Professor Calderwood on Evolution. 
75 
of a seriously perplexing order. These I shall attempt shortly to 
describe, for they do not seem to he at all lessened by the most 
recent investigations and discussions. 
There is practical unanimity — at least ample agreement to sustain 
our scientific conclusion, — concerning the structure and functions of 
the sensory apparatus. We may experience some difficulty in repre- 
senting to ourselves what feeling is, as it appears in the life of a 
snail or of a fish ; but we are at least clear that there is in both 
forms of life sensibility to contact, and such sensibility as proves 
adequate to direct motion. We can similarly interpret sensibility 
along divergent lines, as in the action of the optic, auditory, and 
olfactory nerves in higher life-forms. An animal swerves as readily 
under the influence of light, sound, or odour, as under the whip ; 
there seems no manifestation of intelligence in this, as there would 
be none in the case of a man. But intelligence is something very 
different from sensory impression, whether it is concerned with 
the size of an object, direction of a sound, or the meaning of sign. 
How can we explain the appearance of intelligent action ? 
The functions of the best developed sensory system, seem quite 
inadequate to supply a scientific conclusion here. Even if we add all 
the advantages connected with an exact knowledge of intelligent ex- 
perience, as in our own consciousness, our difficulties are not abated, 
but seem to come out in more perplexing form. Take a series of 
sensory impressions, even according to the possibilities of the highest 
organism, and it seems impossible to find, either in their nature or 
in their relation, anything helpful towards an explanation of the 
rise of intelligence. The sensory apparatus can do no more than 
supply impressions; successive impressions cannot even become a 
series without the action of intelligence in comparing the impres- 
sions. In whatever direction we turn, with the best apparatus in 
most efficient order, we find that intelligent comparison is a necessity 
— a presupposition — in order that any such experience as ours may 
be possible. Impression must indeed follow contact. By the same 
necessity, but with no provision for permanency of the first, or for 
comparison of the two, a new impression must result from renewed 
contact. The history of this is continual rise and fall of feeling, — 
continual flux, — but no meaning. Sensations are continually 
arriving and continually passing away. Even to say as much as 
