OF CARTILAGE. 33 
also accord with the young cells of plants. Compare plate I, 
fig. 8, ff, with fig. 2. The form of the nucleus likewise corre- 
sponds with that of many vegetable cells. In these young cells 
of cartilage, it is presented to the observer as a small oval or 
perfectly spherical corpuscle, having, in many instances, a 
granulous and somewhat yellowish appearance, and containing 
one or two nucleoli. (Compare this with the description of the 
nucleus of vegetable cells in the Introduction.) The nucleus of 
the cartilage-cell appears to be hollow, a fact which has not 
been observed with regard to the cytoblast of vegetable cells,’ 
and the nucleoli lie close upon, or in the neighbourhood of the 
internal surface of its wall, whilst, according to Schleiden, they 
lie deep in the cytoblast of vegetable cells. 
The cartilage-cells, when once formed, appear to be endued 
with the capacity to grow throughout the entire mass of the 
structure. The case is different with regard to the formation 
of new cells. This takes place in certain situations only, on 
the surface of the cartilage, for imstance, or between the last 
formed cells. We have already scen that in the branchial rays 
of fishes, the least developed cells lay at the point, and 
lateral margins. The little rod, which the branchial ray 
represents, does not increase in size by the formation of new 
cells between the original ones throughout its entire length, 
but its extension in the longitudinal direction is produced 
by the development of new cells in the neighbourhood of 
the poimt, and it increases in breadth by the same process 
going on in the neighbourhood of the side walls. It is a 
familiar fact, that the cylindrical bones grow chiefly upon the 
surface and at the end of the shaft. The formation of new 
cartilage-cells usually takes place only in the neighbourhood of 
the surface which is in contact with the organized substance, 
(I refer throughout this passage to that period alone, at which 
the cartilage does not contain any vessels of its own,) but it 
is not exclusively confined to that situation, it may also 
proceed in the intercellular substance between the last-formed 
cells. 
At the period of ossification, the earthy matter is first de- 
posited in the cell-walls, or in the true cartilage-substance, the 
' In a letter which I have received from Schleiden, he informs me that he has 
also found hollow nuclei in plants. 
3 
