FEATHERS. 85 



fore, as follows : a minutely- granulous mass is present in the 

 first instance, in which numerous cell-nuclei lie, some of them 

 exhibiting a nucleolus. Around them the cells are formed, 

 being at first not much larger than the nuclei, and having a 

 granulous aspect. The cells gradually expand ; the nucleus 

 also grows, and soon reaches its full maturity. It remains 

 eccentrical, lying upon the cell-wall. The cell-membrane re- 

 tains its granulous aspect for a time; gradually losing it, 

 however, as the expansion of the cells advances ; at the same 

 time the contents of the cell-membrane become darker, but the 

 cell-walls are not at all diminished in thickness. The walls 

 of the cells, in the next place, become more firmly united 

 together, so that they cannot be separated from one another 

 so readily, and at the same time the nucleus gradually dis- 

 appears. The contents of the cells at last dry up, and they 

 become filled with air. The development of these cells ac- 

 cords, therefore, entirely with the vegetable cells, the nucleus 

 being their true cytoblast ; it is present before the cell, and, 

 as is generally the case in the cells of plants, afterwards be- 

 comes absorbed. The cell expands, growing by intussuscep- 

 tion, and the membrane of the fully- developed cell might, 

 without much danger of error, be assumed to be more than 

 ten times heavier than that of the youngest one. The phy- 

 sical, and probably also the chemical, condition of the cell- 

 membrane undergoes a change. The cytoblastema, in which 

 the cell-nuclei are in the first place formed, consists of gra- 

 nules, analogous to the mucus-granules, in which, according 

 to Schleiden (Miiller's Archiv, 1838, plate III, fig. 2), the 

 cytoblasts of vegetable cells originate. According to Schleiden, 

 those mucus-granules are deposited from a solution of gum 

 within a parent-cell. The cells of feathers are not formed in 

 parent-cells, but in the neighbourhood of the organized matrix. 

 There can be no doubt, however, but that the matrix only 

 exudes a fluid, which afterwards becomes transformed into a 

 granulous substance. I have not investigated the mode in 

 which the nuclei originate in the cytoblastema, whether 

 by a junction of smaller globules, whether the nucleoli first 

 exist, and so forth. The growth of the nucleus proceeds for 

 a time with that of the cell ; for the latter is formed around 

 the nucleus before it has reached its full size. The cytoblas- 



