522 MR. J. T. CARTEK : DENTICLES ON 



crypts at the sides of the bases of denticles already erupted and 

 ^xttached (PI. II. fig. 1, d). 



As these successional denticles grow their predecessors become 

 ■detiiched and shed, their removal being brought about by absorp- 

 tion at the base. In sections of the rostrum there is no trace of 

 the superficial denticles, which consist of typical fine-tubed dentine 

 (PI. II. fig. 2, d) becoming embedded in the substance of the bone. 

 The denticles are larger along the lateral margins than on the 

 upper and lower surfaces. 



The presence of denticles in any Teleostean fish is a point of 

 interest, for the question arises " What part do the denticles 

 play in the development of the bony layer to which they are 

 attached"? Goodrich (Proc. Zool. Soc. 1907, pp. 763-764) 

 states : — " Nor is there any evidence that denticles do ever 

 really contribute to form dermal bones. Even in the case of the 

 palatal bones of fish and amphibians, the teeth do not actually 

 combine to build up the supporting bone, but become fused 

 sooner or later to bony substance independently developed at 

 their base " (the italics are mine). 



On this important point I am unable to agi-ee with Goodi'ich 

 for reasons advanced later in this paper. 



Denticles develop in the soft tissues and usually are supposed 

 to obtain a secondary attachment to the bone, but I am not aware 

 of any detailed account of how such attachment takes place. 

 In the absence of fixed material of older Swordfishes I have 

 had to turn to other fishes to trace out the development of the 

 denticle and its pediment and how attachment between them is 

 ■eftected. I realize the objection can be raised that the conditions 

 obtaining in the case of teeth in the mouth may be adaptations 

 to special conditions, but the manner of development of denticles 

 in Xiphias and Histiophorus, and their mode of attachment, 

 4ippears to be identical with that of teeth in the various areas of 

 the mouth in other Teleosts. 



As in the case of the denticle of Xiphias, the point of attach- 

 ment of the tooth to its pediment is always at the point of 

 junction of epithelium with mesoderm. Whether development 

 takes place in a bony crypt or deep in the soft tissues, far from 

 the surface, it is invariably found that the epithelial inflection, 

 the enamel organ, extends down the whole length of the tooth 

 to the transparent area, where it ends. 



In PI. III. fig. 1, which is a photomicrograph of a section 

 through the pharyngeal plate of a Blenny, a developing tooth is 

 •shown lying beneath the functional teeth. It is seen to consist 

 of a tooth (cZ), a translucent zone (i.~), and a pediment (^)), all 

 forming on the surface of one papilla (d.p). The epithelium 

 (e) is seen to extend down to the limits of the tooth. 



On examining the functional teeth it is apparent that the 

 relationship between the various parts still exists : the teeth are 

 •.still connected, by means of the translucent area (tz), to tlie 

 pediments but now these latter are joined one to another l)y 



