OF CARTILAGE. 2t 
corresponds to the wall of the corresponding cell. This appear- 
ance of strata, however, is observed only in the thick walls 
between two groups of cells, and as these groups probably ori- 
ginate by the formation of two or four cells within a parent 
cell, each half of the partition-wall between two groups must 
(presuming such to be the mode of their formation) consist 
again of two layers, the one of which corresponds to the wall 
of the parent cell, the other to that of the secondary cell, so 
that each partition-wall of two groups must consist of four 
layers. Although it does, indeed, appear that even a greater 
number of layers or strata are present, yet I must at the same 
time remark, that these observations are by no means sufii- 
ciently conclusive for the proof of a fact so important in refer- 
ence to the process of nutrition, and that I am so far from re- 
garding them as evidence of a stratified deposition of the sub- 
stance, as not to hold such a thing to be even probable. The 
appearance is probably an optical deception. As before stated, 
no distinction was found between primary cell-membrane and 
secondary thickening in the cartilages of the branchial rays of 
fishes, but it seemed that the cell-membrane had actually be- 
come thickened ; neither is there any such distinction to be 
observed in the branchial cartilages of the tadpole. 
If the above described groups be assumed to have had their 
origin by the formation of secondary cells within a primary 
parent one, in that case, secondary cells which completely fill 
the parent one have not been developed in all the primary cells, 
for isolated cells occur in the branchial cartilages of Pelobates 
fuscus, which are somewhat larger than the secondary ones, 
but smaller than the other primary cells, and remarkable also, as 
will be seen immediately, from their contents. 
The cells of the branchial cartilages of the larva of Pelobates 
fuscus just mentioned, contain within them one or more nuclei. 
(Pl. I, fig. 8, d.) These nuclei, which may be easily isolated, 
are either slightly oval, or perfectly globular, more or less 
granulous and yellowish, and apparently hollow. They contain 
one or two very distinct, round, dark nucleoli, which lie in 
their interior either close upon the wall, or very near to it. 
The nuclei (a portion of them at least) appear to lie free in 
the cell-cavity, for they may readily be isolated. The above 
mentioned primary cells of the larva of Pelobates fuscus in 
