THE MARSIPOBRANCHIL. 125 
Axolotl and Salamander, by fusion of teeth alone,* and of 
his description of the part played by the teeth in deter- 
mining the characters and limitations of certain other 
bones of the head, suggests that their restriction to and dis- 
appearance over a definitely localized area may have had 
originally to do with the first differentiation of the bony 
jaw-apparatus. Be this as it may, comparison of the 
Marsipobranch with the Sharks named, shows the calcified 
teeth of the former to be more nearly homologous with 
the said diffused denticles, than with those more super- 
ficial ones surmounting the jaws, which become of 
increasing importance in the ascending series of the 
vertebrata and alone remain in the highest members 
thereof. The inherent properties of the stomodzum are 
such that there is no apparent reason why it should not 
give rise to mouth scutes at all points; and, this being 
so, the differences between the calcified teeth of the 
Marsipobranchii and higher gnathostomata would appear 
to be expressive of complete divergence in modification 
from a common type. In the former the buccal scutes are 
restricted to the roof and floor of the mouth; in the latter 
they predominate in relation and are ultimately restricted 
to the jaws. t 
The Marsipobranchii may be thus justly regarded as 
aberrant gnathostomata; but the facts herein stated 
necessitate a modification in the belief of Dohrn and 
Beard that they are descendants of relatively highly 
organized fishes (as judged by the structure of those 
extant). 
* On examination of the advanced larva of S. maculosa I incline strongly 
to the belief that true bone is added at a late period. 
t Parker’s assertion (Phil. Trans., 1882, p. 154) that the developing bones 
of the larval Sturgeon’s mouth are mostly dentigerous, and Ryders recent 
declaration (Bull. U.S. Fish Comm. Vol. VIII, p. 263) that minute teeth 
are present on its pharyngeal floor, render it highly probable that a diffuse- 
toothed stage is passed through by that animal. 
