1900-1 Phison Dis S. Euphrates Boreas Hiddekel Cerberus S. Amenthes Jamuna Cerberus N. Pyramus Cyclops Laestrygon Ganges 28. Deuteronilus Sitacus Adamas 29. Djihoun Gihon 30. Is 1903 Djihoun Typhon Hiddekel Orontes Phison Euphrates 31. Protonilus Gihon 32. Marsias Amenthes Laestrygon Cyclops Gigas *Nilokeras I and II Ganges Deuteronilus 33. Pierius 34. Callirrhoe Jamuna Sitacus 35. Astaboras S. 36. Nar 37. Chaos 38. Aethiops 39. Hyblaeus 40. Eunostos 41. Thoth 42. Nepenthes 43. Triton 44. Pyramus 45. Fretum Anian 46. Vexillum Lethes Cerberus S. 47. Nilokeras I Cerberus N. 48. Tithonius 1905 Nilokeras Ganges Hiddekel Chrysorrhoas Djihoun Sitacus Phison Euphrates Amenthes Vexillum Astaboras S. Adamas Cyclops Cerberus S. Cerberus N. Tartarus 49. [*]Propontis Gigas Gihon Nepenthes Thoth Laestrygon 50. Polyphemus Deuteronilus Triton Eunostos Tithonius Callirrhoe Pyramus Nar Protonilus 51. Naarmalcha In spite of possessing the property of pairing, a canal may not always exhibit it. To the production of the phenomenon the proper time is as essential as the property itself. So far as a primary scanning or first approximation is capable of revealing, a canal will be single at one Martian season and double at another. Thus these canals alternated in their state to Schiaparelli and for the earlier of his own observed oppositions to the writer. In consequence Schiaparelli deemed gemination a process which the canal periodically underwent. Three stages in the development were to him distinguishable: the single aspect, a short confused aspect, and the clearly dual one.