OF ARTS AND SCIENCES. 21 



higher Vertebrata. In the lower classes they are of a much less com- 

 plicated character. Thus in many fishes the concentric lamellce. do 

 not exist, and therefore there has been no linear arrangement of the 

 cartilage-cells. But these cells are ossified in situ, and their canali- 

 culi, radiating thence on every side, give to the whole a most regular 

 and beautiful appearance. 



" The cartilage of the cartilaginous fishes seems to differ from 

 the common cartilage of the higher Vertebrata. In fact, it cannot be 

 called true cartilage, but is, if I may so express myself, an osseous 

 tissue in a cartilaginous dress. 



"This may be explained by a few remarks. Valenciennes* has 

 shown that the cartilage of the cartilaginous fishes and of the Cepha- 

 lopoda contains gelatine, and not chondrine. 



" Miillert has also shown that all cartilage capable of ossification 

 contains chondrine, and not gelatine, and that after ossification no 

 chondrine is found, but all is gelatine. Therefore bones are, so to 

 speak, gelatinous, and not chondrinous ; which, as we have just seen, 

 is also true of the so-called cartilages of the cartilaginous fishes and 

 Cephalopoda. 



" The tissue forming the skeleton of these fishes, as I have had op- 

 portunities to examine it, is composed of oval or spherical cells like 

 those of common cartilage at an early period. They have become 

 hardened in situ, but not calcarified ; and never have I met any hav- 

 ing canaliculi radiating from them. From these data we may conclude 

 that in these lower fishes there is bone-cartilage, but not true bone." 



Professor Agassiz said that he believed naturalists, iti con- 

 sidering organic tissues, were altogether too much in the habit 

 of looking at different tissues as if they were entirely distinct 

 bodies, forgetful of the fact that all are derived from one yolk. 

 In considering the first formation of cartilage, we must look 

 to the formation and development of the dorsal cord. We 

 find these cells differing from the blastodermic cells, in be- 

 ing larger, but bearing no resemblance to cartilage-cells, al- 

 though they form the basis from which the cartilage-cells 

 are built up. He had carefully examined these cells, which, 

 however, presented points of extreme difficulty, but had not 



* Compt. Rend., Nov. 25, 1844. 



t Poggendorff, Jlnnalen, Band XXXVIII. p. 316. 



