R A. E. Crew 169 



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, 



3. Wool is present in the winter coat but absent from the summer 

 one. 



4. The microscopical structure of hair and of wool are briefly 

 described and attention is called to the disposition of the wool in the 

 fleece of 0. orientalis, since this most closely resembles that of the wool 

 of the modern domesticated breeds. 



BIBLIOGRAPHY. 



EwART, J. CossAR (1913). Trayis. High, and Agric. Soc. Scot. p. 160; (1914) Ibid. p. 74. 

 Hatjsmann, L. a. (1920). Amer. Nat. vol. liv. No. 635, p. 496. 

 Lydekker, R. (1912). The Sheep and its Cousins. London. 



EXPLANATION OF PLATES I AND II 



Fig. 1. 0. amnion poli. Summer (left) and winter (right) fleeces, x 1^. In the summer 

 coat the distal two-thirds of the longest hairs are pigmented; young heavily pig- 

 mented hairs form a dark mat upon the skin: there is no wool. 



In the winter coat the hair is longer and the tips are broken; there is much less pig- 

 ment; there are no young hairs; and there is an inner coat of wool. 



Fig. 2. The cortical cells of hair, x 110. (a) The hair of 0. amnion poli; (h) of 0. ammon 

 hodgsoni; (c) of 0. ammon ammon. The pigment is arranged around the cells. 



Fig. 3. The cortical cells of the mature hair of 0. ammon poli. x 450. The ceUs are those of 

 the cortex; there is no overlapping and the cells are arranged in the form of a mosaic. 



Fig. 4. The lateral edge of a full-grown hair, x 420, to show that there is no cuticle. 



Fig. 5. A young hair from the summer coat, x 1230, to show the presence of the cuticular 

 scales. 



Fig. 6. Wool, x 600. (a) O. ammon poli. (b) 0. ammon ammon. (c) 0. ammon hodgsoni. 

 {d) A fibre sho^ving the presence of air-spaces within the medulla. 



Fig. 7. Wool. X 3. To show the disposition of the fibres, (a) 0. orientalis. [h) 0. ammon 

 poli. 



{Received Aug. 11th, 1921.) 



12—2 



