SUMMARY1The fleeces of certain wild and primitive species of sheep were examined.2That of Marco Polo's sheep was found to be the one most suitable for examination, since samples of both summer and winter coats were available. In the former coat there was hair only and still growing. In the latter coat it was mostly full‐grown and much less pigmented. The white appearance was due to the presence of a film of air between the pigment granules of the cortex and the eye of the observer.3Wool is present in the winter coat but absent from the summer one.4The microscopical structure of hair and of wool are briefly described and attention is called to the disposition of the wool in the fleece ofO. orientalis, since this most closely resembles that of the wool of the modern domesticated breed