1889-90.] Professor Calderwood on Evolution. 73 
of life, are well defined. In accordance with these every organised 
being is placed in vital relation with its environment; it is sensitive 
to contact, it is capable of receiving sensory impression, and of 
responding to it in action. This may be represented in simplest 
form thus : — 
Centre of Vital Energy. 
Starting with this simple provision, research is continued along 
the line of increasing complexity in structure, until we find Special 
Senses, with special terminal organs providing for definite modifica- 
tions of the sense of touch, while the elaborate system of nerve- 
fibres is correlated in a nerve-centre of proportionate complexity. 
We come within the region of difficulty and debate when we 
reach the higher orders of animal life, classifying these together 
as we may do in accordance with homologies in structure and 
function. Within this group we may include with man, our higher 
domesticated animals, the cat, dog, and horse, and besides, the 
monkey and ape. 
We are thus brought directly upon the question of animal intelli- 
gence, with all the difficulties of observation connected with it. 
Here at least we have definite evidence of intelligence, for which it 
is needful to account. And this problem is far from easy, in view 
of the forms of life only a little lower. A tendency has appeared 
to seek abatement of this puzzle by the hypothesis that mind is 
present from the first movements of life. There is extreme difficulty 
in interpreting such a suggestion, as we recognise in representing 
mind-manifestation in a gnat, in a worm, or in a mollusc. Besides, 
the hypothesis virtually abandons the scientific conception of 
evolution, giving up the attempt to demonstrate that the appearance 
of intelligence is scientifically explained through elaboration and 
differentiation in the nerve-centres. If it is held that “ psychic ” 
