HINGED TEETH OF THE COMMON PIKE. 3 



is the habit of the pike to prey upon other fish, often of 

 relatively large size, and these can only be swallowed when 

 they are conveyed to the gullet in a longitudinal direction, 

 either head or tail foremost. The fish is taken into the 

 mouth of the pike either uninjured or but slightly maimed 

 by having been seized by the large marginal teeth ; the 

 mouth is then tightly closed, and the prey held up against 

 the palate by the elevation of the tongue and floor of the 

 mouth. In this position the movement of the prey is ren- 

 dered all but impossible, save in one direction ; so long as 

 it lies longitudinally along the median line, between the two 

 palatine bands, its passage backwards to the throat is un- 

 obstructed, the hinged teeth giving way before it ; but move- 

 ment in any other direction is checked by its becoming 

 caught upon the sharp points of teeth rigidly fixed against it. 

 Thus the very struggles of the prey are probably utilised in 

 bringing it into, and arranging it along, the median line of 

 the mouth so that it can be easily swallowed ; during this 

 process, which, unless the prey be small, lasts some minutes, 

 showers of detached scales issue from beneath the gill-covers 

 of the pike, thus giving evidence of the employment of the 

 teeth within its mouth. 



The facts to which I have so far called attention might 

 have been more appropriately detailed elsewhere than in the 

 pages of a microscopical journal, but it seemed desirable to 

 preface an account of the structure of the teeth with a few 

 words describing their manner of use. 



The marginal anchylosed teeth of the pike are familiar 

 microscopic objects, and I need only recall one or two points 

 in their structure. They consist externally of a very thin, 

 apparently structureless layer, probably enamel; inside this 

 comes a tolerably well-marked layer, in which tubes like 

 those of ordinary dentine run out towards the surface, and 

 this is generally described as a layer of hard or unvascular 

 dentine ; inside this, solidly filling up the interior of the 

 tooth, in which there is no axial pulp cavity, comes a coarse 

 calcified tissue permeated by many longitudinal canals (as in 

 fig. 2), the vaso-dentine of Owen, which for reasons detailed 

 elsewhere (' Proc. Royal Soc.,' No. 179, and forthcoming 

 * Phil. Trans.') I prefer to call osteo-dentine. 



It is necessary to briefly describe the development of this 

 internal core, as without so doing one of the most striking 

 peculiarities of the hinged teeth would be unintelligible. 

 In the calcification of the dentine papilla the outer shell of 

 hard dentine (d) is first formed; from its interior rods of 

 calcifying tissue shoot down through the whole substance of 



