THE CATEGORIES OF VARIANT INDIVIDUALS 65 



commended, as they introduce fresh connotations for terms 

 which are beginning to acquire a fairly regular meaning. 



II. Pal^eontological Categories 



Perhaps the most important principle to which we should 

 refer under this heading is the palaeontological ' time-charac- 

 ter ' concept. The status of the species in time is as significant 

 as it is in its modern relationships and is often neglected by 

 neontologists. Of recent years some noteworthy studies have 

 been made on series of fossils in which evolutionary change 

 can be studied intensively through successive horizons. The 

 technique of this study was formulated by Neumayr and 

 Waagen ; but its application to series of closely allied forms 

 has been developed by Carruthers, Rowe, Swinnerton and 

 Trueman in this country. The essence of the procedure is 

 the study through a series of successive horizons of series of 

 closely related forms in terms of their individual characters. 

 The result of such studies is the concept of the lineage and the 

 bioseries. The first is a racial complex of lines of descent, 

 which on account of crossing and biparental reproduction 

 must, as Swinnerton (1930, p. 387) points out, prove to be not 

 a series of parallel evolutionary lines, but a finely meshed 

 network. The bioseries is the historical sequence formed by 

 the changes in any one character and relates to the modifica- 

 tion of any single heritable feature. Each line of descent 

 and each lineage will be composed of numerous bioseries 

 evolving at different rates, just as each individual is composed 

 of different characters. In such developmental series ' tran- 

 sients ' (i.e. individual modes) at stages remote from one 

 another are as distinct as taxonomic species, e.g. in one 

 such lineage the Cretaceous sea urchin Micraster has a stage 

 M. praecursor which could be rated as a distinct species from its 

 successor M. coranguinum. 



There exists some ambiguity as to the relationship between 

 the ordinary systematic concept of species and the lineage. 

 But this much is clear — that although within a given lineage 

 the concept of species is difficult to apply (Trueman, 1930) 

 because of the difficulty of disentangling the series of ' anasto- 

 mosing ' lines of descent, yet a given horizon will contain 

 discrete entities corresponding to systematic species, each of 



