TEETH OF PHYSETER 27 



preceded by a milk dentition, thus conforming to the generally 

 accepted view that (as far at any rate as the facts contained 

 in the present paper allow of a statement) the Cetacea are the 

 offspring of a stock already provided with the typical Eutherian 

 dentition. 



Messrs. Pouchet and Beauregard, as has been duly pointed 

 out in the above pages, register an apparent peculiarity of the 

 developing teeth of P h y s e t e r in the form of tufts of out- 

 growths from either the dental lamina or as a direct series of 

 buds arising — not from, but Ijeside, the dental lamina. These 

 I have not been able to discover in the younger foetus described 

 by myself. But in any case they are not, as I believe, to be 

 regarded as a peculiarity of Physeter or of the Cetacea. 

 For others have dealt with structures which are, I think, 

 essentially similar. 



Thus Leche (3, PI. ix, fig. 70 ; PI. xi, figs. 64, 90 ; PI. xvi, 

 figs. 140-2) figures and refers to a number of small ' tags ' 

 attached to the dental lamina in Phoca groenlandica, 

 in the bat Phyllostoma, and in the marsupial P h a s c o - 

 1 a r c t u s . The latter figures are copied by Wilson and Hill 

 (7, PI. xxxi, figs, 76, 77). How far such outgrowths have any- 

 thing to do with tooth formation — phylogenetically for 

 instance — the facts at my disposal do not allow of a guess. 

 They suggest themselves as a mere state of perhaps abnormal 

 activity. 



There is a final matter, however, in which a possibly important 

 difference from that generally observed in mammals is to be 

 seen in the developing teeth of Physeter macrocephalus. 

 This concerns the continuation along the jaw not only of the 

 dental lamina but of the actual tooth germs of the permanent 

 series only. The more usual state of affairs in mammals must 

 be referred to first. Thus in the earliest stage (Stage II) of 

 the embryos of Perameles studied by them Messrs. Wilson 

 and Hill (7, PI. xxv, figs. 1, 2, and woodcut fig. 1 on p. 475) 

 represent the origin of a third deciduous incisor which grows 

 out of the dental lamina. In the first of these sections the 

 dental lamina is shown alone without a trace of the tooth which 



