The Commemoração, the headwater branch of the Gy-Paraná, on which we were, is a deep river from three hundred to a thousand feet wide, with reddish water and a swift current. It was not necessary for the men to ply the oars except when rounding some sharp bend where steerage-way was required, and this was fortunate, as it rained so much of the time that the men were glad to seek the protection offered by the covered portion of the boat. In the intervals between the deluging showers the sun blazed down mercilessly; trees on both sides of the narrow lane of water sparkled as if bedecked with jewels. In places the forest rose from the river’s edge in sheer walls of variegated green; tree-trunks, brush, and palms united into one solid battlement by mosses, climbing lilies, and ensnaring creepers. Again, clumps of graceful ita-palms leaned far out over the water and then rose in a series of stately, feather-crowned columns. At frequent intervals we had glimpses of the animal life that lurked within the impenetrable barrier of the forest fastness. Monkeys were especially plentiful, and within an hour after starting we had seen four distinct species, representing as many families; there were files of black howlers, the males jet-black, while the females are of a straw-color, moving leisurely through the branches; troops of dainty squirrel-monkeys, with deep-chestnut backs, grayish heads, and white faces, scampered over the tops of the lower trees. Black spider-monkeys sat in the highest crotches and gazed down at us in stupid perplexity, and once we startled a family of woolly little night-monkeys of a grayish color, which had selected a thick clump of overhanging vegetation as their diurnal sleeping-place. Large flocks of blue-and-yellow macaws, flying two by two, crossed the river high overhead, doubtless on their way to some choice feeding-ground. Kingfishers sped away in front of the hurrying _batelão_, and from the depths of the woods came the muffled sound of an ivory-bill’s tapping on a hollow trunk. That night we reached the junction of the rivers Commemoração and _Pimentá Bueno_, the latter a stream not less than a thousand yards wide, with a great volume of water. The river formed by the confluence of these two streams is known as the Gy-Paraná. We had covered a distance of eighty kilometres. In ascending, it had taken the _batelão_ nineteen days to cover the same stretch of river that we had just descended in one day.