28 FRANK E. BEDDARD 



appears suddenly in the next sections as an outgrowth of the 

 dental lamina. There is no trace of any direct connexion — 

 additional to the dental lamina — lietween the germ of this 

 tooth and preceding teeth ; its enamel organ is a separate 

 outgrowtli of the dental lamina. In the same way these 

 authors represent the growth of a premolar in the same animal 

 in a later stage (Stage III). 



There are seven sections figured (a-g), each three sections 

 apart. It is not quite clear what is the exact connexion between 

 the second premolar (represented in figs, a and b) and the 

 dental lamina ; but in any case the latter is shown as such 

 (i.e. without any tooth outgrowths) in figs. c-f. Then in g 

 suddenly appears — as an outgrowth of the dental lamina — the 

 rudiment of deciduous premolar three ; the whole tooth germ 

 — that is, the actual tooth, the dental lamina, and the residual 

 dental lamina, extending beyond the tooth — possessing a close 

 resemblance to one of the teeth of the lower jaw in Physeter, 

 such as is represented in Text-fig. 1 of the present paper. 

 There is no trace here either of any continuous lamina connect- 

 ing the individual tooth germs. A final instance is shown by 

 Woodward in a reconstruction of the teeth, deciduous as well 

 as permanent, of Sorex (10, PI. xxv, fig. 19). In this figure 

 the teeth are seen to depend from the dental lamina , only, 

 and to be completely separate from each succeeding and 

 preceding tooth. Quite different is the state of affairs shown 

 in my sections of Physeter. The processes of the dental 

 lamina which I have identified above with the milk dentition 

 are in fact a series of processes only arising at intervals from the 

 dental lamina. But the permanent teeth are produced at the 

 free end of the dental lamina (in the case of the upper jaw) 

 or from its lingual surface, leaving a continuous residual lamina 

 (in the case of the lower jaw). In the upper jaw the position 

 of the future teeth is shown by a bending inwards of the entire 

 dental lamina (see Text-figs. 6-8), and a thickening of the 

 same at intervals ; but there is no projection of the rudiments 

 of teeth beyond the edge of the dental lamina, which is con- 

 tinuous between the successive teeth and is only different in 



