468 CHARLES S. TOMBS. 



when we get a deutine which ueither presents a vascular caual 

 system nor ordinary dentinal tubes, structures which a wider 

 investigation and the observation of cases in which both co-exist, 

 as in the teeth of Pleuronectidse, seem to stand in a comple- 

 mentary relation to one another. 



To sum up the results of these observations, true dentinal 

 tubes are not met with in the Gadidse. The spear-point enamel 

 tip exists in all of the family, even upon the smallest teeth. 

 Those members of the family which have the largest teeth, 

 either fixed to the jaws by anchylosis (ling, some of the teeth 

 of the hake) or by a highly elaborated hinge (the hinge-teeth 

 of the hake), have the vascular canal system in its highest deve- 

 lopment. Those which have the teeth small in relation to the 

 size of the animal, as happens in a large number of Gadidse, and 

 those in which the teeth are not very firmly attached, show also 

 a simplification of the minute structure of the teeth. But mere 

 smallness of size does not necessarily involve simplification of 

 structure, as is exemplified by the tiny teeth of the gill-rakers 

 of the hake. Nor does large size necessarily involve elabora- 

 tion of structure, as is instanced by the large teeth of Uraleptus. 

 On the other hand, large and small teeth in the same creature 

 present identical structure ; and whilst the differences in tooth 

 structure in some instances follow the lines of the accepted 

 classification of the genera, in others they do not. 



Bibliography. 



1. Tomes, C. S. — "Outlie Structure and Development of Vascular Den- 



tine," ' Pbil. Trans.,' 1878. 



2. Owen, R.—' Odontography,' 1840— 1S45. 



3. IIetzius, as quoted by 'Nasmyth on the Teeth,' 1835. 



4. Tomes, C. S. — ' Dental Anatomy,' fiftli edition, 1898. 



5. GtJNTHEK, A.—' The Study of Fishes,' 1880. 



