16 THE VOYAGE OF H.M.S. CHALLENGER. 



The cement uudoul^tedly owes its origin to the alveolo-dental periosteum, which will 

 serve as a centre of formation of new cement so long as the growth of the shaft 

 continues. It is not possil^le to speak so positively of the origin of the tissue which 

 constitutes the opaque central band of the shaft. If it be, as I have surmised, a 

 modified vaso-dentine, then one would have to look to the pulp for its seat of production, 

 but if it be a modified cement, then it would arise from the alveolo-dental periosteum. 

 In the latter case, therefore, almost the entire shaft would be of periosteal origin. The 

 tooth differs most materially from the tusks of the elephant or the narwhal, in which 

 the pulp-cavity is persistent, and the continuous growth of the tusk is due to the con- 

 version of the pulp occupying that cavity into dentine. 



In the original specimen from the Cape, described and figured by Dr Gray and Ijy 

 Professor Owen, the teeth were not so large as in this animal, in which, indeed, the teeth 

 have attained a size greater than in any previously recorded specimen. Dr Gray states 

 that the length of the anterior edge of the exposed part of the tooth of his specimen 

 was 9| inches, whilst in this one the same border was 10 inches to the base of the 

 denticle, and nearly an inch more to the highest part of the shaft. Nothing is said by 

 either of these authors of the teeth crossing each other on the dorsum of the beak, and 

 in the front view of the teeth in the jaw given by Dr Gray (fig. 72, c) the summits of 

 the shafts are represented as touching, but not crossing. 



From Dr Hector's short account of the teeth in his specimen, which was caught at 

 the Chatham Islands, and from his published figures (PL HI. figs. 1-5), it is obvious that 

 his animal was younger than the specimen B. The teeth in the New Zealand jaw are 

 only 6 inches long and 3 inches wide, so that they could have projected only at the side 

 of the beak and not reached its dorsum. From the notes taken by Mr Moseley, on his 

 visit to the WeUington Museum, I extract the following more complete account of these 

 teeth, and a comparison of their characters with those of the Cape specimen : — 



" "When the anterior margins of the teeth in the two specimens, at the spots where 

 they emerged from the alveoli, are placed accurately side by side at the same level, the 

 posterior margins of the teeth in the New Zealand jaw reach back and correspond in 

 sweep of curve exactly to the vacant alveolar spaces which are conspicuous immediately 

 Ijehind the teeth in the Cape jaw. The teeth in the New Zealand specimen are thus 

 inclined at a less angle than they are in the Cape one, and it appears that the teeth as 

 they increase in age and length, become tilted up towards the vertical, leaving vacant 

 alveolar spaces behind them. Possibly they are dragged up by attempts to open the jaw 

 after they have overlapped. In the New Zealand specimen the dentinal caps (my 

 denticles) are about twice as large as in the Cape one, and proportionately thick and 

 stout. In both, these caps are, when the teeth are in situ, almost vertical in direction, 

 havino- thus, curiously enough, the original direction which they had when within the 

 young alveolus, notwithstanding the curving of the hypertrophied fangs. In the New 



