180 MICROSCOPIC ANATOMY OF THE TEETH 



especially in view of the very remarkable conditions which 

 have been found in many of those already examined. 



An investigation of the development of the enamel in 

 the Gadidse (Cod family) was published by C. S. Tomes 

 in 1900 (266), and a special investigation of the conditions 

 in the Sparidse and Labridse (Sea-breams and Wrasses) was 

 published by the present author in 1917. 



A very curious and anomalous condition is seen in the 

 enamel organ of the Cod family as described by Tomes. 

 In the early stages of development there are no marked 

 peculiarities of the enamel organ ; the odontoblast layer is 

 well developed, and there is a distinct external epithelium, 

 but no stratum intermedium or stellate reticulum separating 

 the two layers, and the enamel organ is enclosed within 

 a definite tooth-sac. In the next stage described, the 

 ameloblasts have entirely disappeared and their place is 

 taken by a delicate reticulate structure. 



A considerably greater amount of forming enamel is laid 

 down than of dentine, in one measurement taken the width 

 of the dentine being 18 /^, while that of the enamel was 90 /m. 

 This, he states, ' is a reversal of the order of procedure 

 obtaining in mammals, in whom the dentine always ante- 

 dates the enamel considerably'. In marsupials, however, 

 a similar condition is seen, the width of the layer of form- 

 ing enamel far exceeding that of the dentine (see fig. 95). 

 C. S. Tomes also describes an appearance of fibrillation 

 within the delicate stroma this fibrillation being arranged 

 at right angles to the dentine and he considers that the 

 appearances are not very different from those which would 

 result from the approximation of thin- walled tubes and per- 

 haps some interstitial substance, a sort of honeycomb with 

 enormously elongated cells. He also states there are no cells 

 visible. Transverse sections are described as showing circular 

 clear spaces surrounded by a stained area in sections treated 

 with hsemalum. He describes abundant blood-vessels in the 

 walls of the tooth-sac, but states that they do not enter the 

 enamel organ. The same author points out that a peculiarity 

 in the development of the enamel in these fish is ' that 

 after the transformation of the ameloblasts into the stroma 

 there are no conspicuous cells to which can be assigned the 



