XVII.] THE PROBLEM OF THE ORIGIN OF SPECIES. 211 



it follows that metamorphism and denudation — fire and 

 water — are incessantly destroying the ancient records of 

 creation; so that all that geologists can ever hope to re- 

 cover are the latest leaves of the volume, and these in but 

 a fragmentary state, because a large proportion are covered 

 by the sea, and others buried inaccessibly deep. 



With all this, it remains true that many intermediate Discovery 

 forms have been discovered ; and, what is a most important °^ "l-*^®^"" 

 fact, no class — no type of form — has been found among forms, 

 fossil species fundamentally unlike all living classes. As 

 has been truly remarked, all fossil forms can be arranged 

 either in or between living groups. To mention what is, 

 perhaps, the most striking instance of this : till very lately, 

 the class of birds appeared to be isolated from all others ; 

 but recent discoveries have proved — or at least all but 

 proved — the former existence of an entire order connecting Reptilian 

 the birds with the reptiles. ^"''l^- 



Another objection to the development theory is that Varia- 

 raised by Dr. Beale, and alluded to in the last chapter ; hlgt^o^,,*'/ 

 namely, that although the forms and external characters gieal 

 of species are variable, there is no proof that their histo- 

 logical or minute structural characters are so. On this 

 subject we are as yet, I believe, quite too ignorant to base 

 any argument, either the one way or the other. My own 

 opinion, however, based purely on the analogy of the case, 

 is this : that . as structure differs between species and 

 between classes, but differs less than form, so it will be 

 found that structure varies within the limits of the same 

 species, but varies less than form. 



Having thus briefly touched on the principal arguments 

 against the development theory, I will go on with those in 

 its favour. I cannot as yet enter on the subject of the 

 process by which the development of new species has been 

 brought about, and its causes ; but I will here state in 

 outline some reasons for believing in the development 

 theory, which are to me of great weight, though they are so 

 far from obvious that they appear to have been unnoticed 

 until tlie publication of Darwin's great work. 



p 2 



