A YORKSHIRE NATURALIST 125. 



When Owen, in his " Odontography," published his 

 notions respecting the way in which the dentine or 

 tubulated substance of the human tooth was deve- 

 loped, he described a very elaborate system of soft 

 structures, by means of which this dentine was 

 produced. Identical tissues are produced in the 

 middle layer of these scales by much simpler 

 methods. A layer of thin membrane, which by 

 calcification in the basal part of the scale is con- 

 verted into bone, ascends into a higher portion of 

 that scale, and being calcified, is there converted into 

 tooth substance. Recent observations demonstrate 

 that the dentine of the human tooth is produced in 

 an equally simple way. My discovery of the simple 

 mechanism by which the formation of tooth structures 

 in fishes was produced, now proves to be equally 

 applicable to all teeth. 



The results of these investigations were laid before 

 the Royal Society in June 1849, an< ^ published in 

 Part II. of the " Philosophical Transactions " for 

 that session. The same memoir dealt with the 

 dermal teeth of the shagreen or skins of the sharks 

 and rays, collectively designated by Agassiz the 

 Placoid fishes. 



I devoted my leisure hours during the remainder 

 of 1849 an d the first half of 1850 to a similar study 

 of the Cycloid and Ctenoid fishes, but I also ex- 

 tended my researches into the structure and develop- 

 ment of the bones, as well as of the integumental 

 appendages of these animals. My results were 



