DENTICLES ON THK SNOUT OF XIPHIAS GLADIUS. 321 



Jl>. On the Occurrence of Denticles on the Snout o£ Xiphias 

 fjladkis. By J. Thornton Carter, (Hon. Research 

 Assistant, Department of Zoology, University of 

 London, University College). 



[Received .June 16, 1919 : Read June 17, 1919.] 

 (Plates I.-III.*) 



The purpose of this communication is to describe the appearances 

 seen in the examination of a portion of the rostrum of a young 

 Xijyhias gladius wfiicli was kindly given bv Dr. Smith Woodward, 

 P.R.S., to Professor J. P. Hill, F.R.S., who handed it to me for 

 report, since I am engaged, under his direction, in an investigation 

 of the histogenesis of dental tissues. 



Sections of the m;iterial disclose the presence of denticles, 

 hitherto described amongst Teleosteans only in various Siluroid 

 fishes. 



These little conical denticles (PI. I. fig. 4, d) are seen to rest on 

 pediments (p) to which they are attached by a substance having a 

 translucent appearance {tz)^ and this area of attachment invariably 

 coincides with the point of contact of epithelium (e) and the 

 underlying connective tissues {m). These pediments are connected 

 with their neighbours by trabeculee (PI. I. fig. 4, tr), and so a 

 continuous bony layer is formed overlying the premaxilla (PI. I. 

 fig. 4, j9?h), with which however it enters, at certain places, into a 

 connection so intimate tliat no line of demarcation is visible 

 (PI. I. fig. 1). Where the section passes transversely through 

 the base of such a pediment it is seen to have an annular shape 

 (PI. I. fig. 2,7;) the lumen of which is occupied by a continuation 

 of the dental papilla. ' 



The denticles develop (PI. I. fig. 3) as is usual, from a 

 mesoblastic papilla which is invested by an. ingrowth of the 

 deeper layer of the oral epithelium to form an enamel organ 

 consisting of a. double layer of cells, the innermost of which is 

 made up of columnar cells, the ameloblasts, whilst the outer 

 layer or external epithelium consists of cuboidal cells. 



I have not been able to procure a portion of the lostrum of an 

 adult Xiphias for comparison with my sections of the young, but 

 Mr. Tate Regan, F.R.S., has kindly given to me a piece of the 

 rostrum from a skeleton of an adult Hisiiophorus and also a 

 fragment of the skin taken fi'om the area, of junction of the 

 rostrum with the rest of the skull. This portion of skin 

 contains, lying in its substance, the small tips of denticles, which 

 would seem to show that they are developed in the same manner 

 as those seen in the sections of Xiphias. 



But, as the I'ostrum elongates, a change occurs in the site of 

 development, for now the forming denticles are seen to lie in 



* For explanation of the Plates see p. 325. 



