DEVELOPMENT. 19 



General Introduction. But in the great majority of fishes, the germs of 

 the new teeth are developed, like those of the old, from the free 

 mucous m.embrane of the mouth throughout the whole period of 

 succession, a condition which is peculiar to the present class. The 

 angler, the pike, and many of our common fishes, illustrate this mode 

 of dental reproduction : it is very conspicuous in the cartilaginous 

 fishes, in which the entire phalanx of their numerous teeth is 

 ever moving slowly forward in rotatory progress over the alveolar 

 border of both upper and lower jaws, the teeth being succes- 

 sively cast off as they reach the outer margin, and new teeth rising 

 in equal proportion from the mucous membrane behind the rear rank 

 of the phalanx. 



This endless succession of new and sometimes, as in Balistes, and 

 Sargus, of highly complicated matrices, — this constant development 

 of a new apparatus for the production of each new tooth, even where 

 its final development is unaccompanied by an eruptive stage, and 

 where the destruction of any part of the formative apparatus is not 

 a necessary consequence of the completion of the tooth, could 

 hardly seem other than a waste of the formative energies to the 

 reflecting physiologist entertaining the doctrine of dental development 

 by transudation, and by whom the dental pulp must have been 

 regarded in the capacity of a gland. The destruction or waste 

 of other glands by no means follows the natural exercise of their 

 functions : the disappearance of the pulp pari-passu with the 

 growth of the tooth, is only an inevitable consequence when that 

 growth is effected by deposition of the calcareous particles in the 

 substance, instead of by transudation from the surface of the formative 

 pulp, and when fresh material is not progressively added to the base 

 of the pulp. In the cyclostomous fishes, where the albuminous, 

 horn-like teeth seem really to be transuded from the pulp, these are 

 persistent ; and the new teeth are formed immediately beneath the 

 old, and from the same surface of the reproductive pulp. 



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