HAIRS OP MONOTREMES AND MARSUPIALS. 577 



Onnthorhyuclius, aud subsequently sinks with the deepening 

 tube. Material by which this suggestion could be tested is 

 unfortunately wanting. But the open tube is not by any 

 means the only, although it is the most important point about 

 the development of the hair of Ornithorhynchus. The great 

 length of the papilla projecting through the bulb into the 

 lower part of the hair is also very significant, suggesting a 

 previous development like that of a scale or feather from the 

 surface of the epidermic covering of a papillary core, traversing 



Fig. D. — Longitudinal section through a hair which is supposed to have 

 develoi)ed on the surface and not in a follicle. The part corresponding 

 to the inner root-sheath is marked by wavy lines. 



m.h. Medulla of hair. c.h. Cuticle of hair. co.h. Cortex of hair. 

 c.i.r.s. Cuticle of inner root-sheath, i.r.s. Inner root-sheath, o.r.s. 

 Outer root-sheath. Mpg. Malpighian layer. 



the structure from base to apex. Further confirmation is 

 aflForded by the axial rod of soft protoplasmic cells forming the 

 medulla of hair ; for a shortening papillary core, surrounded 

 by cells of the rete mucosum superficially undergoing corni- 

 fication, would tend to leave just such an indication of its 

 former presence/^ 



First of all as to the supposed open tube. We have already 

 poiuted out that neither the large nor the small hair of either 



