Sentence:  What we ordinarily term language is made up of vocal signs of an arbitrary character, with corresponding written signs. As general principles are recognized in the construction and arrangement of these signs, we see at once the reason that brutes have no artificial language — that is, no sign that are agreed upon as expressive of ideas. They do indeed have a natural language, made up of natural signs, cries, and motions, which vary in different tribes of animals; but artificial, that is, <WSD>constructed language</WSD>, is a wholly different thing, although it may incorporate into itself features from natural language. The parrot is indeed said to talk, but it is sheer imitation; and he never originates any language. 
Meaning of the word marked with <WSD> tags:  Any language used by people, as opposed to less civilized means of communication, such as the socialization between animals.