In stage (_c_) the sign as eye-picture suggests the name; In stage (_d_) the sign as ear-picture suggests the sound; and it is in the passage from (_c_) to (_d_), whereby constant signs are chosen to stand for constant sounds, that the progress of the human race was assured, because only thereby was the preservation of all that is of abiding value made possible. [Illustration: Fig. 7.--Quipu, for Reckoning, &c.] (_a_) _The Mnemonic Stage._--This is well represented by "quipus" or knotted cords, and by wampums or shell-ornamented belts. The quipu (fig. 7) has a long history, and is with us both in the rosary on which the Roman Catholic counts his prayers, in the knot which we tie in our handkerchief to help a weak memory, and in the sailor's log-line. Herodotus tells us that when Darius bade the Ionians remain to guard the floating bridge which spanned the Ister, he "tied sixty knots in a thong, saying: 'Men of Ionia ... do ye keep this thong and do as I shall say:--so soon as ye shall have seen me go forward against the Scythians, from that time begin and untie a knot on each day; and if within this time I am not here, and ye find that the days marked by the knots have passed by, then sail away to your own lands'" (iv. 98). And the same obviously handy device is of widespread use, reaching its more elaborate form among the ancient Peruvians, from whose language the term "quipu," meaning "knot," is borrowed. It consists of a main cord, to which are fastened at given distances thinner cords of different colours, each cord being knotted in divers ways for special purposes, and each colour having its own significance. Red strands stood for soldiers, yellow for gold, white for silver, green for corn, and so forth, while a single knot meant ten, two single knots meant twenty, double knots one hundred, and two double knots two hundred. Such simple devices served manifold purposes. Besides their convenience in reckoning, they were used for keeping the annals of the empire of the Incas; for transmitting orders to outlying provinces; for registering details of the army; and even for preserving records of the dead, with whom the quipu was buried, as in old Egypt the biography or titles of the deceased were set forth in hieroglyph and deposited in the tomb. Quoting from Von Tschudi's _Peru_, Dr. E. B. Tylor says that each town had its officer whose special function was to tie and interpret the quipus. They were called Quipucamayocuna, or knot-officers; but although they attained great facility in their work, they were seldom able to read a quipu without the aid of an oral commentary. When one came from a distant province, it was necessary to give notice with it whether it referred to census, tribute, war, and so forth. But by constant practice they so far perfected the system as to be able to register with their knots the most important events of the kingdom, and to set down its laws and ordinances. Although vain attempts to