EXPÉDITION ANTARCTIQUE BELGE 



side. The fourth and fifth are distinctly double-rooted, but not so conspicuousl)- as are the 

 corresponding teeth of no. 43-1 1-25-4. 



Of the two Belgica skulls, no. 897 agrées in the number of its cheek-teeth and the charac- 

 ter oftheir roots with no. 43-1 1-25-4. The teeth however, (especially the lower incisors) are rather 

 small. No. 700, on the other hand, présents us with an entirely new combination. In this head 

 there are six teeth on either side of the upper jaw, but hère the splitting process would, I sup- 

 pose, be regarded by Mr. Bateson as having taken place not at the anterior but at the posterior 

 end of the séries. Thus the two last teeth on either side are much smaller than the remainder 

 and, still following Mr. Bateson's assumption, might be taken to represent the fifth tooth of a 

 normal head. The first of the pair is in each case double-rooted ; the second is single-rooted on 

 the left and imperfectly provided with two roots on the right. The remaining teeth of the upper 

 jaw are similar to those of no. 43-11-25-4, except only that the double root of number two is 

 very feebly developed and the small basai notch runs up the tooth as a groove as in no. 324 b. 

 In the teeth of the lower jaw we hâve every gradation from the tapering, single-rooted number 

 one, through the flattened and grooved number two and the slightly double-rooted number 

 three, to numbers four and five, both double-rooted and with, in the latter case, widely separated 

 fangs. 



We hâve hère then a very remarkable instance of variation. Of four skulls two are alike 

 and, following Mr. Bateson, presumably normal. In the two remaining skulls Mr. Bateson would 

 see a very great tendency for the teeth to reproduce themselves. Thus in both, to still follow 

 this supposition, we actually get a new tooth added to the séries, apparently by the (') reproduc- 

 tion of one of the normal teeth, but whereas in no. 700 this occurs on both sides of the upper 

 jaw and the tooth which has reproduced itself is the last of the séries, in no. 324 b it is the first 

 tooth of the séries which is affected and that only imperfectly on one side. In the lower jaw of 

 the same spécimen both the first cheek-teeth are imperfectly divided and possess double crowns. 

 Amongst the other teeth any stage of the splitting or reproductive process may be found 

 from a simple tooth with one root through a single-crowned double-rooted or single-rooted 

 double-crowned tooth to a pair of single-rooted or even double-rooted teeth. The latter, however, 

 still keep up their réminiscence of the supposed splitting process by being together only about 

 equal in size and substance to the ordinary single tooth which they represent, a truly unexpected 

 state of things, from which it would almost appear that a tooth with two roots may be halfway 

 on the road to become two teeth. 



The teeth of Ommatophoca, besides furnishing data for conclusions somewhat of the kind 

 hère indicated, hâve supplied Mr. Bateson with the material upon which to base an attack upon 

 modem views of the homologies of mammalian teeth, an attack combated at some length by 

 Dr. Kukenthal. In view of the fact that it will be my duty to describe the spécimens brought 

 home by the Southern Cross, I do not propose to add to the discussion opinions based upon 

 scanty material, but must hère rest content with a mère description of the variations which occur, 

 with a passing allusion to the arguments of Mr. Bateson and Dr. Kukenthal. 



DiSTiNGUismxr; Characteristics : ■ - (a) The skull of Ross's seal cannot possibly be 

 confounded with that of any other living Pinniped. Its great resemblance lies with that of Cysto- 

 phora cristata Erxl. of arctic waters. In gênerai size it about equals that of Leptonychotes Weddelli, 



(1) I t;il thi term from Mr. Bateson. 



