140 PHYLLODUS. 



lamelliform tooth of the Phyllodus but these teeth being piled one 

 upon the other, the entire mass presents a succession of strata of 

 the three substances. 



The osseous substance (a, fig. 2, PI. 44), is characterized by the 

 large, reticularly anastomosing medullary canals, without radiated cells 

 in their interspaces, which are peculiar to the structure of the bones 

 and ossified basis of the teeth in fishes. The dentine (&) consists 

 of numerous, close- set calcigerous tubes and the clear uniting 

 substance ; the tubes are characterized by their straight, and parallel 

 course ; at the middle part of the plate, they are directed vertically to 

 its plane, and at the margins which are bent down, they incline so 

 as to maintain the same relative position to that part of the surface 

 of the plate; their diameter does not exceed j^th of an inch; 

 their subdivision into pencils of smaller tubes takes place nearer 

 to the enamel than usual. I could plainly discern the anastomoses 

 of these divisions of the calcigerous tubes in some parts of the sec- 

 tion. The enamel c, which, as in the denticles of the Scarus and 

 many other fishes, closely approximates in structure to the dentine, 

 exhibits, however, much less parallelism in the course of its compo- 

 nent tubes in the Phyllodus ; but these are as numerous and 

 distinct, though somewhat more minute than those of the true 

 dentine. 



It would seem that in the matrices or pulps of both the ena- 

 mel and dentine, the progress of calcification followed the same 

 law, viz : from the circumference to the centre, or from the surface 

 to the attached base of the pulp. In specimens of the Scarus pre- 

 served in spirit, and in other fishes, I find that neither surface of the 

 formative pulps is free, for, while that which may be termed the base 

 of the enamel-pulp is adherent to the capsule, and while the base of 

 the dentinal pulp turned in the contrary direction, coheres with the 

 mucous surface from which it was originally developed, the opposite 

 surfaces of both pulps firmly adhere to one another. It is at this 

 surface, however, in each case that the process of calcification com- 

 mences. The linear groups of cells being here irregular in their 

 position, form, by their confluence, tubes as irregularly disposed ; 

 but as the deposition of the hardening salts proceeds, the tubes 



