570 BAIJJWIN SPENCER AND (iKOIMMNA SWIOKT. 



10; by Poulton are in reality associated with the ituicr root- 

 sheatli. Our material is certainly in a very fair state of pre- 

 servation, and in all the stages examined in which the root- 

 sheath is developed it can be seen most clearly that the latter 

 extends throughout the whole length of the follicle, and at the 

 open end is directly continuous with the middle layers of the 

 epidermis. Possibly the difference in this respect in the 

 various accounts may be due to the fact that at one particular 

 part of the follicle there is a special modification of the sheath, 

 which can be seen by reference to fig. 25. Tiiis represents on 

 a large scale the part of the follicle which is slightly swollen 

 and lies near to the open end. On the upper side of the 

 follicle tiie swelling is more pronounced than on the lower 

 side, and the nuclei of the outer root-sheath, to the special de- 

 velopment of which the swelling is due, are arranged as shown 

 in the figure in a somewhat radiating manner. The most im- 

 portant feature, however, is concerned with a special modifica- 

 tion of the inner root-sheath ; the lumen of the follicle becomes 

 somewhat contracted in this part, and the hair is tightly 

 grasped by the sheath, which itself is somewhat more solid in 

 api)earance than elsewhere, and is also less sharply marked off 

 from the outer root-sheath thau at a lower level. In addition 

 to this, the lower part of the inner root-sheath as shown at x 

 (fig. 25) is slightly produced into a kind of collar arrange- 

 ment, so that on casual observation it might even be thought 

 that the inner root-sheath only extended as far as this point. 

 Anything like a close examination of sections in a good state 

 of preservation shows clearly that there is merely a local 

 differentiation in the sheath, which is again to be associated 

 with the fact that at this spot the hair is tightly grasped in the 

 follicle, and that we are, in reality, as can be seen from an in- 

 spection of the figures, dealing with a continuous structure. 



The whole face of the inner root-sheath is clearly marked at 

 this stage by the downwardly directed serrations which repre- 

 sent the cuticle of the sheath and fit into the upwardly directed 

 ones on the surface of the cuticle. This thin serrated layer of 

 the inner root-sheath is morphologically continuous with the 



