17. Coat and Fibre Development in some British Sheep.

Summary.1. The development of the coat is essentially the same in all breeds examined, viz., Leicester, Southdown, Suffolk down, Oxford down, Dorset down, Scots Blackface, Scots Blackface X Wensleydale, Leicester X Cheviot, Southdown X Leicester, Oxford down X Suffolk down, and Suffolk down X Cheviot.2. Hair follicles in these sheep begin to develop before wool follicles. Wool fibres grow rapidly, and in late fœtuses are arranged in rows at the skin surface and grow faster than the hairs, which show no special arrangement at the skin surface.3. Wool follicles in the breeds examined are spirally shaped. The shape of the basal portion of the follicle largely determines the shape of the fibre produced.4. The development of the wool fibre is essentially the same as that of fibres in mammals generally, but differs in important detail.5. The sudoriferous or sweat gland is differentiated early, and much sooner than the sebaceous or fat gland. The duct of the sudoriferous gland always opens into the follicle.6. The structure of the inner root‐sheath layers of all types of follicles is the same as the structure of these layers in the human hair follicle, as described by A. von Brunn (1).7. Before appearing above the skin, the tip of the young fibre is pushed along a curved passage in the epidermis. This passage is excavated by cells from the sebaceous gland.8. It is shown that during growth of the wool follicle in the Scots Blackface X Wensleydale cross, the level of the arrector‐muscle insertion changes from the lower half to the upper half of the follicle.