C, — GEOLOGY. 73 



IS warranted by the evidence of recapitulation, a fact which further 

 indicates that the change arises by addition or subtraction at the end 

 of the individual life-cycle. So far as I am aware this phenomenon, 

 at least so far as genera are concerned, was first precisely defined 

 by Louis Agassiz in his 'Essay on Classification,' 1857. He called 

 it ' Serial Connection,' a term which connotes the bare statement of 

 fact. Cope in his ' Origin of Genera,' 1869, extended the observation, 

 in a few cases, to species, and introduced the term ' Successional 

 Eelation, ' which for him implied descent. We may here use the brief 

 and non-committal term ' Seriation. ' 



The comparison of the seriation of living species and genera to the 

 seriation of a succession of extinct forms as revealed by fossils was, 

 it seems, first definitely made by Cope, who in 1866 held the zoological 

 i'egions of to-day to be related to one another ' as the different sub- 

 divisions of a geologic period in time ' (Jourii. Acad. Nat. Sci. Phila- 

 delphia, 1866, p. 108). This comparison is of great importance. Had 

 we the seriations of living forms alone, we might often be in doubt 

 as to the meaning of the phenomenon. In the first place we might 

 ascribe it purely to climatic and similar environmental influence, and 

 we should be unable to prove genetic filiation between the species. 

 Even if descent were assumed we should not know which end of the 

 series was ancestral, or even whether the starting point might not 

 be near the middle. But when the palaeontologist can show the same, 

 or even analogous, seriation in a time-succession, he indicates to the 

 neontologist the solution of his problem. 



Here it is well to remind ourselves that all seriations are not exact. 

 There are seriations of organs or of isolated characters, and the trans- 

 ition has not always taken place at the same rate. Hence numerous 

 examples of what Cope called Inexact Parallelism. The recognition of 

 such cases is largely responsible for the multiplication of genera by some 

 modern palaeontologists. This may or may not be the best way of 

 expressing the facts, but it is desirable that they should be plainly 

 expressed or we shall be unable to delineate the actual lines of genetic 

 descent. 



Eestricting ourselves to series in which descent may be considered 

 as proved or highly probable, such as the Micrasters of the Chalk, we 

 find then a definite seriation. Thei-e is not merely transition, but trans- 

 ition in orderly sequence such as can be represented by a graphic curve 

 of simple form. If there are gaps in the series as known to us, we can 

 safely predict their discovery ; and we can prolong the curve backwards 

 or forwards, so as to reveal the nature of ancestors or descendants. 



Orthogenesis : Deter iiiinate Variation. 



The regidar, straightforward character of such seriation led Eimer 

 to coin the term Orthogenesis for the phenomenon as a whole. If this 

 term be taken as purely descriptive, it serves well enough to denote 

 certain facts. But Orthogenesis, in the minds of most people, connotes 

 tTie idea of necessity, of determinate variation, and of predetermined 

 course. Now, just as you may have succession without evolution, so 

 ' v^u may have seriation without determination or predetermination. 



