The first part (1-50) of Book I. has considerable affinities with the eighth, more than half its hymns being attributed to members of the Kanva family, while in the hymns composed by some of these Kanvas the favourite strophic metre of the eighth book reappears. There are, moreover, numerous parallel and directly identical passages in the two collections. It is, however, at present impossible to decide which of the two is the earlier, or why it is that, though so nearly related, they should have been separated. Certain it is that they were respectively added at the beginning and the end of a previously existing collection, whether they were divided for chronological reasons or because composed by different branches of the Kanva family. As to the ninth book, it cannot be doubted that it came into being as a collection after the first eight books had been combined into a whole. Its formation was in fact the direct result of that combination. The hymns to Soma Pavamana ("the clearly flowing") are composed by authors of the same families as produced Books II.-VII., a fact, apart from other evidence, sufficiently indicated by their having the characteristic refrains of those families. The Pavamana hymns have affinities to the first and eighth books also. When the hymns of the different families were combined into books, and clearly not till then, all their Pavamana hymns were taken out and gathered into a single collection. This of course does not imply that the Pavamana hymns themselves were of recent origin. On the contrary, though some of them may date from the time when the tenth book came into existence, there is good reason to suppose that the poetry of the Soma hymns, which has many points in common with the Avesta, and deals with a ritual going back to the Indo-Iranian period, reached its conclusion as a whole in early times among the Vedic singers. Differences of age in the hymns of the ninth book have been almost entirely effaced; at any rate, research has as yet hardly succeeded in distinguishing chronological stages in this collection.