OF THE HAIRS. 



L87 



which form a simple or a double layer {Huxley's la\ 

 are constantly situated internal to the common, and as far as I 



Fig. 72. 



t 



A 



I- 



\ 



have seen, always single, fenestrated layer of cells ; tliey are 

 shorter and broader than the cells which have already been 

 described (0-014 to 0-018'" long, 0006 to 0009'" broad), but 

 are also polygonal, and always possess, at least in the lower 

 half of the root-sheath, distinct elongated nuclei often prolonged 

 into points of 0-004 — 0-006'". The diameter of the whole 

 inner root-sheath is, upon the average, 0-006 — 0-015'", 

 whence it follows, that its cells, of which there arc never more 

 than three layers, are at least 0002 — 0-005'" thick. They arc 

 recognisable at once in their natural position, and by the teasing 

 out of the root-sheath, and are readily isolated by the use of soda 

 and potass (fig. 72), but without swelling up, a character which no 

 less than their great resistance to alkalies altogether, distin- 

 guishes their cells, in common with the epidermic scales of the 

 hairs, from all others. 



At the bottom of the hair-sac the inner root-sheath consists 

 only of a single layer of beautiful, large, polygonal, nucleated 



Fig. 72. Elements of the inner root-sheath, x 350 : A, from the outer layer, 1, its 

 isolated plates; 2, the same in connection, from the uppermost parts of the layer in 

 question, after treatment with caustic soda: a, apertures between the cells, b- 

 B, cells of the inner not-perforated layer, with elongated and slightly notched 

 nuclei; C, nucleated cells of the lowest pari (single layer) of the inner sheath. 



