328 NOTES ON THE STRUCTUKE AND RELATIONS 



the successive development of the animal kingdom during 

 the successive geological periods, as upon tlie physiological de- 

 velopment of individual animals; and, indeed, lean now show, 

 through all classes of the animal kingdom, that the oldest 

 representatives of any family agree closely with the embry- 

 onic stages of the higher types of the living representatives 

 of the same families ; or, in other words, that the order of 

 succession in animals, through all classes and families, agrees 

 in a most astonishing measure with the degrees of develop- 

 ment of young animals of the present age." Such, on this 

 curious and occult subject, are the conclusions of Agassiz -, 

 and in some of the specimens on the table the Society may 

 see, more distinctly, perhaps, than in any others yet found, 

 two of the marked peculiarities of structure on which the 

 conclusions are based. Let us see what it is these peculiarities 

 actually tell. 



To an external framework of a high order there was added 

 in these ancient ganoids an internal framework, partly, or in 

 whole, cartilaginous. Such, let me remark, is the fact : all 

 the rest is hypothesis. In the Acanths, and all the Cephalas- 

 pians save one genus, the whole internal skeleton was car- 

 tilaginous, and has, in consequence, disappeared. In some 

 of the Celacanths, the portions of the internal skeleton that 

 formed the basis of the double fins, such as the ischiatic 

 bones, to which the ventrals were attached, and at least the 

 ulna and the style-like bone (clavicle) of the pectorals, were 

 osseous j but we find no trace of the vertebral mechanism, 

 whether vertebrae or apophyses. Again, in the Coccosteus, — 

 the one exceptional genus of the Cephalaspians to which I have 

 referred, — we find curiously-jointed apophyses, but no verte- 

 brae. Now, there is no doubt a certain vague analogical sense 

 in which we may term the peculiarity of a cartilaginous ver- 

 tebral column embryonic. Cartilage in the embryo makes its 

 appearance before bone. First, mere gelatinous threads harden 



