OF THE EARLIER GANOIDS. 327 



Lakes) and the sturgeon. " The sturgeon and the white 

 fish," he says, " are two very different fishes ; yet, taking 

 into consideration their external form and bearing merely, it 

 might be questioned which of the two should take the highest 

 rank ; whereas the doubt is very easily resolved by an exa- 

 mination of their anatomical structure. The white fish has 

 a skeleton, and, moreover, a vertebral column, composed of 

 firm bone. The sturgeon, on the contrary, has no bone in 

 the vertebral column, except the spines or apophyses of the 

 vertebrae. The middle part, or body of the vertebra, is car- 

 tilaginous; the mouth is transverse, and -underneath the head; 

 and the caudal fin is unequally forked, while in the white fish 

 it is equally forked. If, however, we observe the young white 

 fish just after it has issued from the egg, the contrast will be 

 less striking. At this period the vertebrae are cartilaginous, 

 like those of the sturgeon ; its mouth also is transverse, and 

 its tail undivided. At that period the white fish and the 

 f sturgeon are therefore much more alike. But this similarity 

 is only transient : as the white fish grows, its vertebrae become 

 ossified, and its resemblance to the sturgeon is comparatively 

 slight. As the sturgeon has no such transformation of the 

 vertebrae, and is in some sense arrested in its development, 

 while the white fish undergoes subsequent transformation, we 

 conclude that, compared with the white fish, it is really in- 

 ferior in rank." Thus far Agassiz's foetal principle of classi- 

 fication. In his recent singularly interesting work, " Lake 

 Superior," we find him thus referring to it, and to the blended 

 character, high and low, foetal and reptilian, of the early 

 fishes. " They may be said," he states, " to have embryonic 

 peculiarities, in addition to their reptilian character ; and this 

 fact, so simple in itself, and apparently so natural, is of the 

 utmost importance in the history of animal life. It has gra- 

 dually led me to more extensive views, and to the convictioD 

 that embryonic investigations ight throw as much light on 



