723 



111 what precedes the chief characteristic of the iiatiiie of the (ooth- 

 chaiige in mammals has also been indicated: the endostichical row 

 expels the exostichical, in other words the two rows succeed one 

 another, there is a change of series. This form of tooth- change will 

 therefore be distinguislied as "slichobolism". With Reptiles the change 

 mnst have an entirely dififerent character, as here the two rows 

 constitute simnltaneouslj' the functionating dentition, so that there 

 can be no question of substitution of one series bj another. .So with 

 Reptiles the change is of a much more elementary character. In this 

 group the productivity of the teeth-band does not stop with the 

 Anlage of a single exo- and endostichical dental series. On the 

 contrary, after the endostichical series has been evolved, a 

 third series appears which must be considered as the substituting 

 series of the first evolved exostichos. After this a fourth appears 

 which will replace the first endostichos and so on. The elements of 

 these subsequent series are formed by the matrices from which the 

 first two series came forth, in this wa^' that a matrix first produces 

 an element for the first exostichos, then for the second exostichos 

 and so on. The second product of a matrix is destined to expel and 

 replace the first and is in ils turn expelled by the third product. 

 All the products of the same matrix may be distinguished as a 

 dental family. With Reptiles every tooth is therefore to be considered 

 as a generation that will be replaced by a following younger generation, 

 produced by the same matrix. So an exostichical tooth will always 

 be expelled by an exostichical one. Consequently there are as many 

 matrices in the teeth-band as the dentition has functionating teeth. 

 These matrices go on producing continuously. With some Reptiles 

 the lime between the formation of two dental generations is longer, 

 with others shorter, but there is no question of a change of series, 

 as the series functionate simultaneously. Here the change has the 

 characteristic that the members of a family, successively produced 

 by a matrix, replace each other. In contradistinction to the stichobolism 

 of the M,onodelpliian mammals I propose lo distinguish this process 

 as "inerobolism". 



What is now the relation between the mammalian dentition in 

 which only once an exo- and endostichical series is evolved and 

 the reptilian dentition in which a number of exo- and endostichical 

 series succeed each other like as many generations? The simplest 

 conception is that with Reptiles the dental matrix extends its produc- 

 tivity over the whole life of the individual, giving birth each time 

 to an elementary tooth, while on the other hand with Mammals the_ 

 whole prodiiclivity of a dental matrix is exhausted in the formation 



