576 



BALDWIN SPENCER AND GEORGINA SWEET. 



to have been originally developed on the surface; then the 

 relationship of the parts can be represented in Fig. D. 



The difference between ourselves and Mr. Poulton lies in the 

 fact that he regards the inner root-sheath as " a true part of 

 the hair itself, and with it arising from the bulb;" whilst^ with 

 the advantage of a larger series of stages than Mr. Poulton was 

 able to study, and with probably better preserved material, we 

 have been led to the conclusion that the inner root-sheath is 

 not a true part of the hair itself, and is not developed from the 



Fig. C. — Longitudinal section through the hair of a Monotreme lying in its 

 follicle, showing the relationship of the layers. 



bulb, a conclusion which our figures — all drawn under the 

 camera lucida — will, we think, serve to demonstrate. It ap- 

 pears to us that the relationship now described renders unten- 

 able the suggested homology between the inner root-sheath 

 and the appendicular parts of a feather. 



We must, however, now return to a consideration of the 

 early stages of the development of the hair. Mr. Poulton 

 (p. 183) says, " It is, indeed, by no means improbable that the 

 first and earliest trace of the hair is formed at the surface in 



