THE DEVELOPMENT OP THE TEETH. 121 



so far as my own investigations go, no connection has been 

 traced between the germs of teeth of different ages ; but 

 Heincke says that in the Pike new enamel organs may be 

 derived from older ones. 



This independent origin of an indefinite number of teeth, 

 having no relation to their predecessors, is only certainly 

 known to occur in the osseous fish : of the development of 

 the teeth of Ganoid fish nothing is known. 



The oral epithelium, which varies much in its thickness 

 and in other characters in different fishes, sends down a 

 process which goes to form an enamel organ, whilst a dentine 

 papilla in rising up to meet it, comes to be invested by it as 

 with a cap. The after- history of the process depends much 

 on the character of tooth which is to be formed. If no 

 enamel, or but a rudimentary coat of enamel, is to be formed, 



FIG. 59 ( l ). 



the cells of the enamel organ remain small and insignificant, 

 as in the mackerel. If, on the other hand, a partial invest- 

 ment of enamel is found upon the perfected tooth, such 

 for instance, as the little enamel tips upon the teeth of the 

 eel (see Fig. 90), then the after-development of the enamel 

 organ is very instructive. 



( l ) Tooth-germ of an eel. d. Neck of enamel organ, e. Enamel cells. 

 a. Cap of enamel, b. Cap of dentine, e. Rudimentary enamel cells 

 opposite to that part of the dentine germ where no enamel will be formed. 



