562 BALDWIN SPENCER AND GEORGINA SWEET. 



in which they lie being marked off by a more or less definite 

 line from those lying to the outside. This layer, which is a 

 more or less clearly marked feature in all stages from the 

 present onwards, represents the cuticle of the hair. Both in 

 this section and elsewhere along the course of the hair the 

 pigment passes continuously round the structure and is never 

 confined to the under side, as Poulton found it to be in his 

 preparations and as it is in the adult hair ; nor after long 

 searching over many hundreds of sections have we been able 

 to find up to this stage any thickening of the cuticle on the 

 upper surface such as is figured by Poulton in his figs. 19 

 and 25, and such as again exists in the adult hair (fig. 3). 

 The cuticle is a clearly marked layer with large nuclei, and is 

 a striking feature in sections, both transverse and lougitudinal, 

 from this stage onwards. 



Immediately outside the cuticle layer lies a series of flat- 

 tened nuclei which stain darkly and correspond to those which, 

 in the previous stage, we described as representing the cuticle of 

 the inner root-sheath. Outside this layer lies a series of layers 

 arranged concentrically with regard to the central papilla and 

 with nuclei which follow the trend of the layers, and as a 

 general rule showing chromatin material in contact with the 

 outer membrane, the inner part of the nucleus being generally 

 devoid of stained material. These layers are, when traced 

 upwards, seen to be directly continuous with the corneous 

 inner root-sheath. There is not at this level, or indeed at this 

 stage of development, any distinction of the inner root-sheath 

 into an outer and an inner part corresponding respectively to 

 Henle's and Huxley's layers, though, as Poulton has already 

 clearly indicated in his descriptions, such a distinction can be 

 easily seen at a later stage and in a part of the inner root- 

 sheath close to the bulb. We are quite of Poulton's opinion 

 when he says (p. 167) with regard to this differentiation that 

 '' it does not, in Ornithorhynchus at least, imply any differen- 

 tiation of the siieath into layers, and when we consider the 

 immense development of the structure in this animal it seems 

 possible that the distinction can hardly be sustained through 



