Development and Growth of the Epidermis. 85 



addition of a transparent border to the last-described nucle- 

 ated granule. The periphery of this transparent border is 

 bounded by a dark interstitial substance, which gives the bor- 

 der a defined outline ; and in the latter situation I imagine a 

 cell-membrane to exist. I am not satisfied, however, that 

 this is the case; and the difficulty of isolating these cells, and 

 their roughness of outline when separated, serve to prove that 

 if a membrane be really present, it must be exceedingly thin 

 and easily torn. Assuming therefore, from analogy rather 

 than from demonstrative evidence, that there exists a boun- 

 dary membrane to the bodies I am now describing, I have 

 termed them " cells ; " the cavity of the cell I apprehend to 

 be the "transparent border," the "nucleated granule" is the 

 nucleus of the cell, the "aggregated granule" of the latter 

 the nucleolus, and the entire body a "nucleolo-nucleated 

 cell." 



Before quitting the structure of the "nucleolo-nucleated 

 cell," or primitive cell of the epidermis, there is a point of 

 much interest to be mentioned with regard to it, which is, that 

 the "transparent border" just described is itself a tier of 

 "aggregated granules." The nucleolus therefore is an "ag- 

 gregated granule," the nucleus a tier (taking its flat surface) 

 of "aggregated granules" surrounding the former, and the 

 cell a tier of " aggregated granules " enclosing the whole. 



To return to the mosaic-like plane of the under surface of 

 the epidermis, the largest of the pieces composing this plane 

 are the nucleolo-nucleated cells. These are placed without 

 order, some being closely pressed together, others being se- 

 parated by moderate intervals, and here and there some sepa- 

 rated by interspaces equal to the breadth of the cells. The 

 interspaces, or intercellular spaces, are occupied by the "nu- 

 cleated granules," "aggregated granules," and "primitive 

 granules," irregularly set in a homogeneous interstitial sub- 

 stance, which fills up all vacuities. The granules and inter- 

 stitial substance modify the light transmitted through them 

 variously at different foci of the microscope ; sometimes the 

 granules look dark while the interstitial substance is light, and 

 sometimes the reverse is the case. 



Such is the structure of the mosaic-like plane of the under 

 surface of the epidermis, and so far, my observations, having 

 reference to facts, are demonstrable and admit of being spoken 

 to positively. The interpretation of the facts I would willingly 

 leave to others, but feel that I am called upon to state any 

 opinion, founded on the above observations, that 1 may have 

 formed of the signification of these appearances. In the first 

 place, then, I must acknowledge myself wholly divided between 



