﻿240 BRITISH FOSSIL CEPHALOPODA. 



fortuitous resemblance to those most nearly allied to them — rests, when truly 

 examined, on no more rational foundation than the more recent and diametrically 

 opposite opinion. I say " opinion " advisedly, for there is proof on neither side ; but 

 prejudices derived from other things than science have been in favour of the first, 

 and every prejudice derived from the study of life itself is in favour of the last. It 

 is for this reason that I have adopted the method of describing actually, not a 

 species, but a single type specimen, round which the other individuals designated by 

 the same name may cluster as closely as they can. In attempting to explain as 

 best we may the undoubted phenomenon of distinct specific groups at the present 

 day, we have practically two theories to choose from — that which considers each 

 species a special creation, or which at least considers them real though inexplicable ; 

 and that which asserts the development of one from the other by a process of evolution. 

 In deciding between these, an appeal is made to Palaeontology to show, if it can, the 

 gradations between one species and another ; and at the close of such a study as the 

 present, the author may well be asked, what is his result from this point of view? 

 In reply, I must state that if species were such definite entities as they were once 

 supposed to be, they ought to be much more easily distinguished than they are ; and 

 the many variations of form which will be found included, and necessarily included, 

 under one specific title, whose " general description " thereby becomes one of 

 considerable latitude, show that different specimens are either not so closely linked 

 as that theory would imply, or else that we ought to adopt many more " species," in 

 many cases one for each individual. The present study is therefore all against 

 fixity of species. Does it, on the other hand, give any positive aid to the theory of 

 evolution ? In considering the true answer to this question, it must be observed 

 that everything which renders the independence of specific forms improbable, in 

 exactly the same proportion makes their dependence probable. If, therefore, the 

 wide variations which are here noted from any specific type renders the fixity of 

 species in any sense improbable, they so far teach that one type is derived from the 

 other. The two views of their origin are, in fact, mutually exclusive. Farther 

 than this it is not very safe to go ; for, among the many forms which flourish in 

 any one epoch, it is impossible to say with certainty which was the descendant of 

 any particular form in the preceding epoch, especially as the intervening links are 

 in all probability absent. It would not be difficult to pick out a series which 

 may have been produced by descent. Thus Orthoceras coralliforme of the Bala 

 period might, by loss of transverse ornaments, turn into Orthoceras Bacchus, which 

 first appears in the Llandovery, and has transverse ornaments in youth ; and this 

 again might change by the longitudinal ornaments becoming all equal, as they 

 begin to be in old age, into Orthoceras Jilosum, which is not found for certain below 

 the Wenlock Beds. But there is no proof that this series is actually so connected, 

 and there are many isolated forms whose ancestors and descendants are alike 



