566 BALDWIN SPENCER AND GBORGINA SWEET. 



place, but in early stages there is no indication of any dermic 

 structure to be seen in the medullary region immediately 

 above the papilla. 



Poulton says (p. 153), in speaking of the hair of Ornitho- 

 rhynchus, " From the tip of the papilla, at any rate in the larger 

 hairs, an axial rod of soft protoplasmic cells, deeply staining in 

 reagents, is continued. This, when dry and shrivelled, admits 

 the hair and forms the characteristic medulla ;" and again, " the 

 great length of the papilla projecting through the bulb into the 

 lower part of the area is also very significant, suggesting a pre- 

 vious development like that of a scale or feather from the surface 

 of the epidermic covering of a papillary core traversing the 

 structures from base to apex/' 



In the first place, we have been quite unable in either 

 animal to detect during development any such axial rod of 

 deeply-staining cells in the medulla, and certainly during the 

 early stages of development no such structure is present ; nor, 

 despite the suggestive appearance of the papilla, as seen in lon- 

 gitudinal section, can any upward prolongation of it be seen in 

 transverse sections of later stages, of which a typical one is 

 represented in fig. 26. Until a certain stage in development 

 has been reached there is no such upward prolongation of the 

 dermis in either Ornithorhynchus or Echidna, and we are 

 inclined to draw from this fact the conclusion that, if there 

 does take place, as perhaps there may, though we have failed 

 to convince ourselves of its existence, any such extension of the 

 dermic papilla into the medulla, this is to be regarded as a 

 secondary feature associated with the special modification of 

 the large hairs, and has no phylogenetic significance. 



However, to return to the structure of the follicle and bulb. 

 By means of the method adopted by Norris and Shakespeare, 

 and used also by Mertsching, which consists in staining with 

 a mixture of Mayer's hseraalum, indigo and carmine, the 

 various layers become well differentiated, though we have not 

 been able to obtain the strong carmine stain indicated in 

 Mertsching's beautiful figures, all the nuclei in our prepara- 

 tions being stained with hsemalum. As a further differentia- 



