No. 3.-] CHEEK AND SNOUT OF AMIA CALVA. 427 
established for them, by Leche, Rose, and others, in mammals 
also. It is thus evident that while, if Hertwig, Klaatsch, and 
Rose are right, the teeth-bearing bones of animals can contain, 
genetically, but one component, they may, or must, contain two 
such components if Walther and Carlsson are right. Klaatsch’s 
observations on the development of the canal bones of teleosts 
seem to indirectly confirm the presence of these two com- 
ponents, notwithstanding the fact that he himself makes such 
a positive statement to the contrary. 
The canal bones of fishes, that is, all those bones that are 
traversed by the canals of the lateral-line system, are said by 
Klaatsch (No. 22, pp. 203, 211) to be developed directly from 
scleroblastic cells proliferated in direct connection with the 
sense organs contained in the canal or canals by which the bone 
is traversed. This origin of the bones definitely excludes, 
according to him, all possibility of that part of these bones that 
immediately surrounds the canal being formed, in any part even, 
by the fusion of dermal teeth or teeth-bearing plates. Where 
the bone traversed by the canal is large, and extends: for some 
distance on one or both sides of the line of the canal to which 
it is related, such distant parts either arise from scleroblastic 
cells that have migrated thither from the related sense organs 
as proliferating centers ; or the bone adjoining the canal under- 
goes an enormous development and displaces — “‘auf Kosten ”’ 
is the expression used —other neighboring bones that may 
perhaps have arisen in connection with dermal teeth. The 
possibility of other bones of somewhat different origin preéxist- 
ing in these regions is thus admitted. 
With these conclusions of Klaatsch, and also with the state- 
ments of facts on which they are based, the observations and 
conclusions of certain other writers are not entirely in accord. 
Walther (No. 46, pp. 66, 78) considers the frontal and nasal 
bones of teleosts, both of which are traversed by lateral canals, 
as of connective-tissue origin, but phylogenetically derived from 
tooth-bearing plates ; and he says of the frontal of Esox (No. 
46, p. 72) that that part of the bone of the adult that encloses 
the lateral canal to which it is related, begins its development 
as two little processes rising perpendicularly from the surface 
