14 



ARKIV FOR ZOOLOGI. BAND i. NO 2. 



spite of the primitiveness in several respects of the White 

 whales it is therefore impossible to assume a DelphinajMrus- 

 like form among the ancestors of the typical Dolphins, but 

 it must be taken for certain that both have develo]3ed inde- 

 pendently form more primitive whales and in such a case it 

 appears necessary to retain Delphinapteridce as a separate 

 family among the toothed whales. 



To make sure about the fundamental differences in struc- 

 ture between the teeth of DelphinajMrus and those of the 

 typical members of Delphinidce I have 

 prepared sections through teeth of Delpliinus 

 delphis, Sieno frontatus, Glohicephalus melas, 

 and Phoccena phoccena and found the fol- 

 lowing. 



The tooth of Delpliinus delphis which 

 was seetioned measured about 15 mm. in 

 total length (conf. fig. 5). The large pulp- 

 cavity which is vvider in its upper portion 

 extends exactl}^ through half the length of 

 the whole tooth and is sharply defined. 

 The conical somewhat curved crown is co- 

 vered by a rather thick cap of enamel, which 

 is thicker on the outer than on the inner 

 side. On the outer side its thickness amounts 

 to 0.180 mm. but on the inner side to 0, 1 2 6 

 mm. Towards the base of the crown the 

 enamel gradually becomes thinner and ceases 

 altogether about 6 mm. from the tip. Not 

 quite one millimetre from the lower margin 

 of the enamel the layer of cement which 

 covers the root begins. This layer of cement 

 increases somewhat towards the middle of 

 the root but it does not appear to attain a 

 greater thickness than about 0,o7 5 mm., 

 thus much less than the enamel. At the base of the root 

 the layer of cement bends round the margin into the pulp- 

 cavity a little. The remainder main part of the root as well 

 as the crown consists of dentine. The solid dentine of the 

 crown has the usual appearance except that bloodvessels 

 extend far into the interiör only leaving the outermost com- 

 pact layer of a thickness of about 0,6 mm. intact. This layer 



Fig. 5. Longitu- 

 dinal section through 

 a tooth of Delphinus 

 delphis. e enamel, d 

 dentine, c cement. 



