Next I think it probable that the advance of receptual intelligence which would have been occasioned by this advance in sign-making would in turn have led to a development of the latter—­the two thus acting and reacting on each other until the language of tone and gesture became gradually raised to the level of imperfect pantomime, as in children before they begin to use words.  At this stage, however, or even before it, I think very probably vowel sounds must have been employed in tone language, if not also a few consonants.  Eventually the action and reaction of receptual intelligence and conventional sign-making must have ended in so far developing the former as to have admitted of the breaking up (or articulation) of vocal sounds, as the only direction in which any improvement in vocal sign-making was possible.”  Romanes continues his sketch by referring to the probability that this important stage in the development of speech was greatly assisted by the already existing habit of articulating musical notes, supposing our progenitors to have resembled the gibbons or the chimpanzees in this respect.  Darwin in his great work on the “Expression of the Emotions” points to the fact that the gibbon, the most erect and active of the anthropoid apes, is able to sing an octave in half-tones, and it is interesting to note that Dubois considers his Pithecanthropus Erectus is on the same stem as the gibbon.  But it has lately been shown that some animals much lower in the scale than monkeys, namely, rodents, are able to produce correct musical tones.  Therefore the argument loses force that the progenitors of man probably uttered musical sounds before they had acquired the power of articulate speech, and that consequently, when the voice is used under any strong emotion, it tends to assume through the principle of association a musical character.  The work of anthropologists and linguists, especially the former, supports the progressive-evolution theory, which, briefly stated, is—­that articulate language is the result of an elaboration in the long procession of ages in which there occurred three stages—­the cry, vocalisation, and articulation.  The cry is the primordial, pure animal language; it is a simple vocal aspiration without articulation; it is either a reflex expressing needs and emotions, or at a higher stage intentional (to call, warn, menace, etc.).  Vocalisation (emission of vowels) is a natural production of the vocal instrument, and does not in itself contain the essential elements of speech.  Many animals are capable of vocalisation, and in the child the utterance of vowel sounds is the next stage after the cry.