FEATHERS. 85 
fore, as follows: a minutely-granulous mass is present in the 
first instance, in which numerous cell-nuclei lice, 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- 
tas 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 walis 
of the cells, im 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 im 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 origimate. 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- 
