88 Mr. E. Wilson's Observations on the 



containing in its interior secondary cells, tertiary cells, nu- 

 cleolo-nucleated cells, nucleated granules, aggregated gra- 

 nules, and primitive granules. 



It will be observed that this hypothesis of cell growth differs 

 from that of Schwann. The theory of Schwann always ap- 

 peared to me to be incompetent to the explanation of the 

 growth of the large scale of epidermis and epithelium in a 

 tissue manifestly subjected to considerable pressure. I sought 

 in vain for the watch-glass cells, elliptical cells, and globular 

 cells in the epidermis; but my search has been rewarded by 

 the discovery of the above-described beautiful process of form- 

 ation and growth. It will be seen that, according to this 

 view of the growth of the epidermic cells, they never possess 

 anything approaching to a globular shape, that the scales are 

 not flattened spheres, but on the contrary always possessed a 

 flattened form, and have increased by a peripheral growth. 

 This mode of growth again is made manifest by the observa- 

 tion of a vertical section of the epidermis. The most careful 

 examination can distinguish no difference between the size of 

 the deeper and the superficial strata of cells ; they have all the 

 same average thickness, all the same average length, — an ap- 

 pearance easily explained when we regard them as parent- 

 cells containing secondary and tertiary cells of the same ave- 

 rage size as the cells of earlier formation. It is true that the 

 complete size of a cell is very quickly attained, and that its 

 growth, taking place in the deepest stratum of the epidermis, 

 could not be expected to produce any difference of character 

 in the middle and superficial strata ; but this is not mentioned, 

 as far as I know, by Schwann. 



The process of growth here described explains also the fact 

 of the disappearance of the nucleus in the scales of epidermis. 

 The outermost granules of the nucleus have become the nuclei 

 or nucleoli of secondary cells, and have consequently been 

 moved away from their original position in the performance 

 of their office of centres of growth to secondary cells. The 

 original nucleus, therefore, is not lost, but merely robbed of 

 some of its component granules, which may be discovered in 

 many parts of the epidermic scale, instead of being concen- 

 trated in a single mass. In these scales, and particularly in 

 epithelial scales, the central and dense part of the original 

 nucleus is generally perceptible; in the latter it constitutes 

 the scale nucleus; and in the epidermic scale there is always 

 some one little mass larger than the rest, particularly if the 

 scale have been for some time immersed in fluid, as when it 

 is examined in the serum of a blister. In an epidermic cell, 

 measuring Q^th of an inch in long diameter, I found several 



