In justice to other observers I must say, however, that I am inclined to believe that in all beetles the antennæ in some way aid or assist audition, but they are adjuncts, as it were, and not absolutely necessary. It is a matter of easy demonstration to show that some of these insects hear less acutely where they are deprived of their antennæ. I presume they are about as necessary in audition as are the external appendages of the human ear; this, however, is mere supposition, and has no scientific warrant for its verity.
I have purposely said but very little about the senses of touch, taste, and smell in this discussion of the senses in the lower animals. These three senses have been so exhaustively treated by Lubbock in his _Senses, Instincts, and Intelligences of Animals_, that I could not hope to introduce any new data in regard to them. Graber, Frey, Leuckart, Farre, Hertwig, and a host of others have likewise investigated these senses most thoroughly.
As to the senses of sight and hearing, the matter presented a different aspect. I was confident that I could add somewhat to the knowledge already formulated, consequently I have treated these senses at some length. Technicalities and the details of microscopic investigation, especially microscopic anatomy, have been omitted; they have no place in a work like this.
Conscious determination, or, effort induced by conscious volition, is the basic mental operation upon which is reared that complex psychical structure which is to be found in the higher animals, and especially in man--the highest product of evolutionary development.
By conscious volition is not meant that consciousness which appertains to the child of two or three years, who, at that age, recognizes the _ego_. Ego-knowledge, while undoubtedly present in some of the higher animals, such as the dog, monkey, horse, cat, etc., is not a factor in the psychical make-up of any of the lower animals (insects, crustaceans, mollusks, etc.). But consciousness, so far as volition or choice is concerned, enters into the _psychos_ of animals exceedingly low in the scale of animal life.
We have seen in the chapter on the senses in the lower animals, that animals possess one or all of the five senses--touch, taste, smell, sight, and hearing; we will see in a later chapter that some of them likewise possess certain other senses which man has lost in the process of evolution.