HATES OF MONOTREMES AND MARSUPIALS. 567 



tion we have found it useful after over-staiuing to reduce with 

 picric acid, the result of which is to render still more clear the 

 variations in the amount of cornification undergone by the 

 various layers. The most corneous layer, that is the stratum 

 corneum, and the side of the inner root-sheath in contact with 

 the hair, stain a brilliant green which shades off into a yellow 

 tint as the cornification becomes less in the deeper (morpho- 

 logically) lying parts (figs. 24 — 26). In this way it is clearly 

 seen that no modification has taken place in the very base or 

 rim of the bulb, which is formed of an outer layer with elongate 

 nuclei and an inner part with rounded nuclei. In this part we 

 have been unable to obtain a clear demarcation of cell outlines 

 such as Mertsching figures,^ though this may perhaps be due to 

 the fact that our specimens were preserved merely in strong 

 alcohol. As, however, we pass up from the base of the bulb into 

 the region of the cuticle and inner root-sheath, there is clearly 

 seen in parts an indication of cell outlines around the nuclei. 

 The layers which in life rest upon the dermic papilla are 

 directly continuous upwards with the medulla and cortex of 

 the hair, and are marked by a strong deposit of pigment. 

 Immediately outside these there is a most clearly marked layer 

 in which the nuclei are larger and more round than elsewhere. 

 Passing upwards this layer becomes resolved into a single 

 series of very distinctly marked cells set at an angle to the 

 surface of the cortex of the hair and developed equally all 

 round ; in the lower parts specks of chromatin can be seen in 

 the nuclei, then at a higher level the latter become flattened 

 and more darkly stained all over, and gradually above the level 

 of the top of the papilla the cell outlines and nuclei disappear 

 and the layer passes up into the strong cuticle with its well- 

 marked serrations. Just above the tip of the papilla there is a 

 definite contraction of the hair, followed by a slight expansion, 

 and then above this it tapers gradually away to the tip, which 

 has just protruded beyond the surface. Outside of and in 

 contact with the cuticle there can be detected three distinct 

 layers in the inner root-sheath ; next to the cuticle of the hair 

 » ' Arch. f. Mikr. Auat.,' Bd. xxxi, p. 32, Taf. 4 and 5. 



