34 SHARKS. 



given off nearly at right angles, but are relatively smaller and shorter 

 than in Lamna. The calcigerous tubes in the body of the tooth form 

 a fine but inextricable moss-like reticulation ; those at the periphery 

 are straighter, and run parallel to one another, and vertical to the 

 outer surface. A stratum of fine calcigerous cells receives the termi- 

 nations of these peripheral tubes, and intervenes between them and the 

 dense enamel-like exterior covering of the tooth. 



In the great fossil teeth of the Carcharias megalodon, the calcige- 

 rous tubes, at the superficies of this tooth, are disposed in groups 

 which, with an insufficient magnifying power, appear like single 

 coarse tubes ; but with a higher power are seen to be composed of 

 congeries of parallel tubes, apparently twisted together. The inter- 

 spaces are nearly equal to the diameter of these fasciculi : they are 

 occupied by more scattered tubes, and by short oblique or transverse 

 anastomosing branches. Atone part of a section of this tooth, which 

 was sufficiently transparent to be examined with the highest powers, 

 the peripheral coarse sinus or canal, which always runs parallel with 

 the superficies, gave off an infinite number of minute tubes, which 

 formed a plexus, (or plexiform stratum), and from the outer part of this 

 plexus, the tubes above described, passed, at right angles, to the sur- 

 face. In the longitudinal section of this tooth, the twisted appearance 

 above described of the peripheral calcigerous tubes was seen to be 

 due to the number of side branches given off at an acute angle, and 

 obliquely to the main tube. At the apex of the tooth, the marginal 

 calcigerous tubes radiate, as in the Lamna, and suddenly diverge to 

 proceed transversely to the sides. In the body of the tooth, the main 

 canals are surrounded by concentric lamellae, traversed by radiating 

 and anastomosing calcigerous tubes, which form a tine net-work in 

 the interspaces of the medullary canals. 



In the flat lancet-shaped teeth of the lower jaw of the Scymnus, 

 the texture of the tooth presents a closer correspondence with that in 

 the higher organized animals, in consequence of the principal or me- 

 dullary tubes being relatively smaller, more aggregated, straighter, and 

 more parallel in their course, than in the sub-genera of sharks just 

 described. These tubes advance in two fasciculi from the osseous 

 bifid base ; the median tubes sUghtly converge and proceed straight 



