108 COMPARATIVE RETROSPECT. 
developed. On the other hand, a formation of cells also takes 
place within the true cartilage-cells, but it is probable that 
they have a different signification from those within which they 
are generated. A deviation from the previous class seemed to 
occur with respect to the spot at which the young cells are 
formed, in relation to the entire tissue. In the former class, 
so far as we could perceive, they were formed at that part 
only where the tissue was in immediate contact with the 
organized substance. The formation of the new cells im 
cartilage, it is true, did not take place throughout the entire 
thickness of the tissue, but (so long at least as the cartilage 
itself is not furnished with vessels) only near the sur- 
face, and therefore, at the spot where it was in contact with 
the organized substance; still, however, it not only took 
place at that point of contact, but went on also between 
the cells most recently formed, as if cartilage had a greater 
capacity of imbibition, so that the cytoblastema penetrating 
from the blood-vessels into the parenchyma arrived at the 
deeper seated portions of the tissue more speedily ; and, there- 
fore, retained its fresh plastic force even in that situation ; 
or, as if the cartilage itself possessed a higher vitality, and, 
therefore, the cytoblastema retained its productive power for 
a longer period, although penetrating quite as slowly as in 
the previous class. 
Although the modifications in the form of the cells of this 
class vary but slightly from those of the preceding one, yet we 
see two striking changes in the cells and their cytoblastema, 
namely, the coalescence of the cell-walls and ossification. The 
thickening and transformation of the cell-walls were very dis- 
tinct in the last class, for example, in feathers. Here a still 
more strongly-marked thickening of the cell-walls takes place 
in several cartilage-cells. The external contours of the walls, 
however, gradually disappear in such instances, and a coales- 
cence takes place to such an extent as to leave merely the 
cell-cavities perceptible, lying in an homogeneous substance. 
The blending of the cell-walls takes place either between the 
walls of neighbouring cells, in instances where they are in 
immediate contact, or, with the intercellular substance, when 
the cells are surrounded by it. Further investigations are re- 
quired in order to decide the question as to whether this 
i te ee et a te a a i ll 
eS oa. oe 
EE ried tile te ae 
