LUCIOIDS. 133 



It is somewhat unusual in the present class, to find such an immense 

 number of teeth, so variously disposed over the parietes of the 

 mouth, yet presenting so uniform a shape ; but all are here adapted 

 to pierce, seize, and retain a living prey, and are thus in perfect 

 conformity with the predaceous habits of the species. The fully 

 developed and functional teeth are attached by a confluence of their 

 bases with the surface of the jaw-bones, and not, as in Sphyrcena, 

 with the parietes of an alveolar cavity. The germs of the succes- 

 sional teeth, also, instead of being developed in alveolar cavities, 

 complete their growth in the original seat of their formation, viz. the 

 vascular membrane or gum, which covers the dentigerous margins of 

 the jaws. 



That the formation of a tooth is an act of conversion of the sub- 

 stance, and not of cells upon a formative surface of the pulp, is 

 clearly illustrated in the Pike. The cone-shaped cap which the half- 

 developed tooth forms upon the remaining matrix can only be 

 removed by overcoming a certain resistance, and this resistance is 

 seen to be due to the processes of the pulp which extend into the 

 medullary canals of the tooth ; the broken ends of these processes give 

 an irregular surface to the exposed pulp, and their continuation into 

 the tooth may be seen by sawing the latter across. This connection 

 between the substance of the tooth and of the pulp is still better 

 demonstrated in a finely injected specimen : the mechanical relation 

 between the tooth and the pulp is then seen to be of precisely the 

 same kind as those between an ordinary osseous nucleus and the car- 

 tilaginous matrix in which it is developed : it is in the course or direc- 

 tion of development that the chief difference exists ; in the tooth 

 it is centripetal, in the bony epiphysis centrifugal ; but the mode of 

 development is the same. In both cases a soft and vascular model 

 and framework of the future hard part is prepared : in it the cells are 

 formed and the tubes are excavated according to the plan destined 

 for the future arrangement of the calcareous particles ; which arrange- 

 ment is not one of indiscriminate diff'usion, but accords with the best 

 known mechanical principles, and is in prospective harmony with 

 the peculiar resistance which the calcified part is destined to over- 

 come. A vertical section of the matrix of a Pike's tooth and the 



