Now, the first point to be noticed about the doubles is that bilateralism, or the quality of being double, is not a universal trait of the canals, either actually or potentially; it is not even a general one. Out of the four hundred canals seen at Flagstaff, only fifty-one have at any time displayed the quality; that is, one eighth roughly of the whole number observed. This point is most important; for the fact is of itself enough to disprove any optical origin for the phenomenon. The characteristic of doubling so confidently ascribed by those who have not seen it to general optical or ocular principles proves thus the exception, not the rule, with the canals, and by so doing disowns the applicability of any merely optical solution. We shall encounter many more equally prohibitive bars to illusory explanation before we have done with the doubles, but it is interesting to meet one in this manner at the very threshold of the subject. On the other hand, the characteristic when possessed is persistent in the particular canal, _in posse_ if not _in esse_. Once shown by a canal, that canal may confidently be looked to at a proper time to disclose it again. In short, bilateralism, or the state of being dual, is an inherent attribute of the individual canal, as idiosyncratic to it as position and size. The catalogue of canals possessing this property, so far as they have been detected at Flagstaff to date, number fifty-one if we include in the list wide parallels like the Nilokeras I and II. Eight of these were observed in 1894; nineteen more were added in 1896, making twenty-seven; in 1901 the total was raised to thirty; in 1903 to forty-eight; and in 1905 to fifty-one. Arranged by years they are tabulated below, where the numeral to the left registers for each its first recording and the position held by it in the list. The starred canals much exceed the others in width, and possibly denote a different phenomenon. DATE CONFUSED 1894 1. Ganges 2. Nectar 3. Euphrates 4. [*]Nilokeras I and II 5. Phison 6. Asopus 7. Jamuna 8. Typhon 1896-7 Ganges Typhon Euphrates Avernus S. Phison 9. Lethes Jamuna 10. Dis S. 11. Titan 12. Laestrygon 13. Tartarus 14. Cocytus 15. Sitacus 16. Amenthes 17. Adamas 18. Cerberus N. 19. Cerberus S. 20. Cyclops 21. Gelbes 22. Erebus 23. Avernus N. 24. Gigas 25. Alander 26. Gihon 27. Hiddekel