EXPLANATION OF THE PLATES. 



to differ solely from the epidermis of the negro in 

 the smaller number of pigment cells contained in it. 

 Ols. Pigment cells and granules frequently exist in the fibres 

 of the external surface of the sclerotic of some ani- 

 mals, as the. pig ; and it is probable that in some 

 instances they may be found in those of the eye of 

 man. 



