150 CYPRINOIDS. 



means does nature ensure in the often repeated process, that the 

 detached osseous parts in the fish sliould always be well set, and 

 the tooth transferred, not only to its right place in the series, but to 

 its right relative position upon the bone ? The marvel is not diminished 

 when we consider that immobility is quite impracticable during the 

 uniting process, that the fish must eat with the teeth that remain 

 fixed, and that the bone to which the new tooth is in process of 

 becoming anchylosed must be daily rotated backwards and forwards. 



The pharyngeal bones in the Cyprinoids have rarely the thick- 

 ness adequate to the lodgment of the matrix of a tooth beneath the 

 one in place ; in this respect they differ materially from those of the 

 Labroid fishes : they are, on the contrary, in general, so thin that 

 they are perforated on the side opposite the anchylosed base of the 

 teeth in place, and the nerves and vessels of the remaining pulp 

 pass by these orifices directly into the cavities of the teeth. 



In all the Cyprinoid fishes the pulp-cavity of the pharyngeal tooth 

 is extensive, and traverses almost the whole of the tooth in the 

 barbel and other species, where the teeth present the elongated laniary 

 form.- The whole of the dentine is composed of fine calcigerous 

 tubes, analogous to the structure of that of the simple mammalian teeth: 

 these tubes in the barbel radiate from the narrow and elongated pulp- 

 cavity, with a general course at right angles to the surface of the tooth, 

 and consequently to the axis of the tooth : their diameter is jeroooth of 

 an inch at their origin with interspaces of thrice that diameter ; they 

 proceed with a slightly but regularly undulating course, branching 

 dichotomously, but not frequently ; and the branches, after slightly 

 diverging are continued nearly parallel with each other, and in the 

 direction of the trunk, until they approach the peripheral and denser 

 portion of the tooth ; here they diverge and decussate each other, 

 and present a general inclination towards the base of the tooth. In 

 plate 58, fig. 1 is shown the origin of a portion of the calcigerous 

 tubes from, and in connection with, the uncalcified portion of the 

 formative pulp, magnified 600 linear diameters ; the honeycombed 

 surface of the pulp, from which some of the calcified tubes have been 

 displaced is shown at the lower part of the figure. The clear calcified 

 walls of the tubes are scarcely, if at all, discernible in sections, which, 

 like the present, are taken parallel with their axis ; and the calcifying 



