OF CARTILAGE. 21 



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 suffi- 

 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. 

 (PI. 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 



