Within their natural range the Caribou apparently resort to practically every type of terrestrial and aquatic habitat (other than cliffs and precipices). On the Barren Grounds proper they frequent the open summits and slopes of the ridges, the dwarf birch thickets, the sedge bogs, and the peat bogs. Their trails traverse all the upland spruce and tamarack tracts, the wooded muskegs, and the willow thickets along the rivers. In the summer and fall they swim the rivers and the narrower lakes, and during the winter and spring they cross these on the ice. They do not avoid rapids; in fact, they seek the shallower ones as fords, and they swim the deeper ones (_cf._ Clarke, 1940: 88). They also cross the tundra ponds on the ice, but probably walk around these smaller bodies of water, as a rule, when they are not frozen. While they may prefer to approach the river crossings over open slopes, they do not hesitate to maintain trails through the dense thickets of willow on the banks. The winter habitat of the major part of the Barren Ground Caribou population comprises the Hudsonian and upper Canadian Zones. This forested habitat is characterized by sparser and smaller timber in the Hudsonian Zone and by denser and taller timber in the Canadian Zone. Important among the features of this winter habitat are the frozen surfaces of the lakes and rivers, where the Caribou are wont to congregate for their daily periods of rest (_cf._ Mallet, 1926: 79; Ingstad, 1933: 86). _Trails_ The favorite migratory highways are the long, sinuous ridges that stretch across the Barren Grounds in a sufficiently approximate north-south direction to serve the needs of the Caribou. Here their age-old trails are particularly in evidence and may even be detected from the air. A single small ridge may bear half a dozen or more such trails (fig. 1), roughly parallel but anastomosing at frequent intervals. They probably change but little from generation to generation. They provide the smoothest courses available, avoiding rocks and shrubs and traversing intervening bogs at the most suitable points. The summits of the ridges constitute vantage points from which the animals may keep a wide lookout for Wolves and human enemies, and on which they may obtain the maximum benefit from fly-deterring breezes. Man himself is glad to utilize these trails, whether on the Barrens or in the timber tracts, wherever they lead in a direction he desires. They are kept open by the hurrying feet of hundreds or thousands of Caribou every year. Along a well-used trail extending through low Barrens near Duck Bay, I found a certain grass (_Agrostis scabra_) growing. I did not recognize or collect it elsewhere during the season. Is this perhaps like certain other species, such as _Juncus tenuis_ (_fide_ Dr. Edgar T. Wherry) and _Eleocharis baldwinii_, in curiously thriving on beaten paths?