1895.] into the Measurable Characteristics of Plants, tye. 377 



which has been supposed by many naturalists to be of great im- 

 portance in evolution, and the present case is therefore worthy of 

 discussion. 



The following suggestion is offered as an explanation of the large 

 negative deviations. As shown in Fig. 1, there are normally five teeth 

 in the dentary margin ; but occasionally (in over 1 per cent, of 

 individuals) only four teeth occur. The reduction in teeth may 

 apparently be effected in various ways : sometimes it is impossible to 

 say that one tooth rather than another is missing ; and the case then 

 resembles those cases of variation in the segmentation of a vertebral 

 column, for example, recently discussed by Bateson (" Materials for 

 the Study of Variation," passim, especially, however, p. 124). In 

 other cases, the reduction appears to be effected by a process re- 

 sembling the filling up of the interval between two teeth, so that the 

 pointe of the teeth proj ect only very slightly. A careful outline of a 

 specimen exhibiting this condition is given in fig. 7. It is evident that 



FIG. 7. 



in this case the little tubercle S which indicates the position of the 

 fifth tooth is the point from which the measurement should be taken ; 

 but if the obliteration of the fifth tooth had progressed but a little 

 further, no indication of its presence would remain ; and the dentary 



