740 Dr. J. BEARD 



scales of Anguis possess a bony basis. And thus here again it is not 

 difficult to see that it is the so called enamel organ, which has become 

 the horn-producing organ. But need we stop here ? Hairs and feathers 

 are ultimately related to horny scales, and the formation of a hair sac 

 has analogies at least to the formation of a horny tooth sac in Petro- 

 myzon. And so, once more, one may venture the hypothesis that 

 hairs and feathers are substitutions of the scales of fishes. Not direct 

 substitutions, as the teeth of Fetromyzon are, but indirectly derived 

 from them through stages, some of which still exist in the horny 

 scales of Reptiles, but others of which are perhaps unknown. 



Returning to Fetromyzon, there seems to be now no doubt that 

 the horny teeth are degenerate products of teeth exactly like those of 

 the Myxinoids, and it is very significant to notice that it is just that 

 epithelium, usually believed to be the enamel-forming organ in true 

 teeth, which is concerned here in the formation of horn. 



Thirty five years ago Prof. Huxley (12) tried to estabhsh the view 

 that the whole tooth is an enderonic formation and that no part of 

 it owes its origin to the enamel epithelium. The discoveries here 

 recorded tend to support his view. Without entering into a discussion 

 of the literature of tooth development, one or two objections to the 

 current view may be here urged. 



Firstly, as others have noticed, the enamel in nearly all cases 

 only arises under a very small portion of the enamel epithelium. In 

 other words, by far the greater portion of the enamel epithelium is 

 certainly not concerned in enamel formation. 



Then again the disappearance of the enamel epithelium on the 

 enamel formation can be explained in other ways , i. e. increase of 

 pressure and absence of nutrition. 



Lastly, the fact observed by Spee (20) viz that certain particles in 

 the enamel epithelium reduce osraic acid in the same way as does 

 enamel, need not be evidence of the enamel-forming function of that 

 epithelium. They may have absorbed those particles (assuming them 

 to be enamel), for purposes of nutrition. The position of the enamel 



the horny scales is ossified, and the body has a complete armor of bony 

 scutes, corresponding in form with the scales" (Huxley 11, p. 186). 

 It is hardly necessary to consider here all those cases of recent or 

 fossil reptiles in which the body is furnished with bony scutes, but the 

 opinion may be expressed that the possession of bony scutes in all these 

 cases is a more primitive condition than that in which horny scales 

 alone are present. 



