of the Tooth-Rudiments in Rodents. 323 



agrees in a remarkable manner with Cope's derivation of the 

 Eodents, as quoted above, — or whether it must be eoiisi(K'red 

 as tlie remnant of the germ of a precursor of the large incisor. 

 Unfortunately the material furnished by the actual results 

 does not entirely suffice for a decision between these two 

 alternatives. 



The development of the rudimentary tooth, as 1 was able 

 to follow it continuously in Lepus, by no means agrees in its 

 main features with that of a milk-tooth, whether, in respect of 

 the relation between the development of a milk-tooth and that 

 of the permanent one, we accept the older view, which is 

 reproduced in the text-books, or that which is held by Bauuie. 

 So far as I am aware, no case is known in which the enamel- 

 organ of a milk-tooth appears directly united with that of its 

 successor, as MM. Chabry and Pouchet have already slio wn 

 to be the case in Lepus, at least with regard to the rudimen- 

 tary tooth of the lower jaw. In the premaxilla the French 

 authors failed to observe the stage in question ; I was able to 

 show that here, at any rate at first, the same thing takes place 

 in Lepus. 



In a superficial examination of the question, the conditions 

 pertaining to the second deciduous incisor in the premaxilla 

 of Lepus tell very much against the assumption that the 

 rudimentary tooth likewise belongs to the milk series. The 

 deciduous incisor referred to is clearly a true precursor of the 

 second and smaller ])ermanent incisor. It attains a high 

 degree of development at a time when the germ of the per- 

 manent i. 2, which at all events proceeds from the adjoining 

 portion of the dental fold, is still quite small and insignificant. 

 It is not until the last stage of foetal life that the permanent 

 /. 2 becomes more strongly developed and displaces the 

 deciduous i. 2, which drops out shortly before or after birth. 



Now are we to suppose that in Lepus the second incisor has 

 retained a true milk-tooth as its precursor, while in the case of 

 the first incisor the milk-tooth remains in quite a rudimentary 

 condition, and is outstripped unusually quickly by the germ 

 of the permanent tooth, Avhich appears at the same time as, or 

 even earlier than, that of di. 2 ? It is true that in explanation 

 of this divergence we can adduce the necessity for a more 

 speedy development of the permanent i. 1 (which, indeed, 

 represents the actual large incisor), whereby to a certahi 

 extent its precursor is deprived of the necessary material for 

 development, and is prevented from passing beyond a rudi- 

 mentary condition. 



Finally, we must also confess that it is more easily 

 imaginable that the enamel-organs of a milk-tooth and its 



