Miss Agnes Crane — Evolution of the BracMopoda. 73 



ancestry of the horse were predicated and have since been actually 

 discovered in a fossil condition. 



Daring the eight years that elapsed between the publication of the 

 English edition of " What is a Brachiopod ? " in 1877 (29) and that 

 of his "Summary of the British Fossil Brachiopoda," in 1884 (28), 

 it is surprising that Davidson had not modified his opinion on the 

 matter. We find him stating (p. 386 et seq.) that he still found 

 the subject of the descent with modification of the Brachiopoda 

 " beset with so many apparently inexplicable difficulties that year 

 after year has passed away without my being able to trace, in a 

 satisfactory manner, the descent with modification among the 

 Brachiopoda which the Darwinian theory requires." He appears 

 at most to have admitted a kind of "dual control" — species some- 

 times modified themselves ; genera originated in a different manner. 

 But, really, the supervision of generic creation and extinction would 

 have been no sinecure. 



" It is probable," — we now quote verbatim, — " that at least a large 

 proportion, if not all of so termed species, may be nothing more 

 than modifications of shapes by descent of a limited number of 

 primordial types ; but it is very difficult in the present state of our 

 information to show passages between the genera among the Brachi- 

 opoda,^ so well as among other groups of animals, which the theory 

 of Evolution absolutely requires" (28). 



In 1894:, thanks in a great measure to the life-long researches of 

 James Hall and the sagacious labours and enlightened views 

 of John M. Clarke, Palaeontologists to the Geological Survey of 

 New York, it is no longer possible to deny the existence of such 

 passages between many of the Palaeozoic genera. Much of the 

 evidence was i-eally accumulated by both Barrande and Davidson, 

 although they failed to recognize its full significance (38, 39, 40, 41). 



The Evolution of the Brachiopoda was the subject of frequent 

 friendly discussions between Mr. Davidson and myself, but we never 

 agreed upon it, for being ultimately convinced of the general appli- 

 cation of the law of the Evolution of organic life on the. earth, a 

 sense of humour prevented me from considering the Brachiopoda 

 as specially created for brachiopodists to describe. My views were 

 sufficiently indicated in an article contributed on the Molluscoida 

 (Brachiopoda and Bryozoa) (16) to the fifth volume of " Cassell's 

 Natural History," in 1881. But it is one thing to assert, a priori, 

 the logical postulate : another to substantiate it by cumulative 

 testimony, as Hall and others have recently done. Truly, as Paley 

 has well said, "they alone discover who prove." 



One great stumbling-block in Davidson's way was his strong 

 belief in the immutability of genera. This conviction is fully ex- 

 pressed on p. 391 of his "Summary" before referred to (28). In 

 a footnote he gives a list of 23 Tertiary and Cretaceous genera 

 regarded as valid by foreign authors, and rejects their claims to 

 generic rank. Of these 23, twenty at least are now recognized by 



^ The italics are my own. 



