250 DENTAL REPRODUCTION IN FISHES. 



dental characters, from tlie rest of the scomberoid family, 

 and proportionally approach the sauroid type. 



In all fishes the teeth are shed and renewed, not once 

 only, as in mammals, but frequently during the whole 

 course of their lives. The maxillary dental plates of 

 lepidosiren, the cylindrical dental masses of the chima3roid 

 and edaphodont fishes, and the rostral teeth of the saw- 

 fish (if these modified dermal spines may be so called) are, 

 perhaps, the sole examples of " permanent teeth" to be 

 met with in the whole class. In the great majority of 

 fishes, the germs of the new teeth are developed like those 

 of the old, from the free surface of the buccal membrane 

 throughout the entire period of succession ; a circumstance 

 peculiar to the present class. The angler, the pike, and 

 most of our common fishes, illustrate this mode of dental 

 reproduction ; it is very conspicuous in the cartilaginous 

 fishes (Fig. 60, e. g.), in which the whole phalanx of their 

 numerous teeth is ever marching slowly forwards in rota- 

 tory progress over the alveolar border of the jaw, the 

 teeth being successively cast oft' as they reach the outer 

 margin, and new teeth rising from the mucous membrane 

 behind the rear rank of the phalanx. 



This endless succession and decadence of the teeth, to- 

 gether with the vast number in which they often coexist 

 in the same fish, illustrate the law of "vegetative or irre- 

 lative repetition," as it manifests itself on the first intro- 

 duction of new organs in the animal kingdom, under 

 which light we must view the above-described organized 

 and calcified preparatory instruments of digestion in the 

 lowest class of the vertebrate series. 



