612 THE AMERICAN NATURALIST. [Vou. XXXIII. 
the conditions under which they were obtained are so meagerly 
given. For the appraisal of such work it is of the first importance 
that the reader should know that the conditions of experimentation 
were beyond cavil, for in any scientific investigation the whole sig- 
nificance of the evidence may turn upon the observance of appar- 
ently slight precautions, and scarcely a hint is here given of the 
methods and control of conditions by the investigator. The book is 
throughout — if we except the detailed and patient analysis of nerv- 
ous structure and sensory processes in the lower orders of life — 
rather observational than experimental, and the author is inclined to 
rely upon an interpretation of significant incidents instead of extended 
and systematic tests. 
In regard to several of the author’s conclusions criticism may be 
entered. Dr. Weir has made many interesting observations concern- 
ing the location and acuteness of the sensory organs in the lower 
animals, but when among these senses he proposes to include 
tinctumutation and letisimulation, I must demur. Color-change 
is a reaction upon a particular environment, not a perception of the 
nature of that environment, and is no more a sensory process than 
is the flight of an insect to escape the sudden leap of a toad. Sen- 
sory is contrasted with motor as perception with reaction. The 
color-change may depend upon a sensory stimulus as does the action 
of the insect escaping the toad, and the function may cease upon the 
extirpation of certain nerve centers, — either sensory, by which it 
becomes insensible to the change in the environment, or motor, by 
which it becomes unable to adapt itself to that change, — but it is 
not, therefore, more of a sensory process than is the reactive adjust- 
ment of the insect. The writer must go much farther than this to 
prove his point, for the establishment of a connection between motor 
function and nerve-center activity does not evince even the existence 
of an accompanying sensory process. The whole function might be 
a reflex form of activity without accompanying consciousness. 
Dr. Weir objects to calling this function an instinctive one, but 
unless he should maintain that it is an adjustment empirically 
acquired by the individual, in thus establishing its dependence upon 
a sensory process he has but proved its analogy to all instincts, 
which are essentially perception-reactions, and differ from acquired 
habits only in the nature of their origin. The impulse may or may 
not be accompanied by awareness of its significance, but this com- 
ment in no way affects its character as an instinctive impulse. 
In his treatment of letisimulation the author reduces it to the 
