THE BRITISH FOSSIL BRACHIOPODA. 387 



descent with modification. All those forms which have come down from an ancient 

 period very slightly modified ought, I think, to be omitted; and those forms alone 

 considered which have undergone considerable change at each successive epoch. My 

 fear is whether the Brachiopoda have changed enough. The absolute amount of 

 difference of the forms in such groups at the opposite extremes of time ought to be 

 considered, and how far the early forms are intermediate in character between those 

 which appeared much later in time. The antiquity of a group is not really diminished, as 

 some seem to think, because it has transmitted to the present day closely allied forms. 

 Another point is how far the succession of each genus is unbroken from the first time it 

 appeared to its extinction,- with due allowance made for formations poor in fossils. I 

 cannot but think that an important essay (far more important than a hundred literary 

 reviews) might be written by one like yourself, and without very great labour." 



In several subsequent letters Darwin reiterated his suggestions ; and, although I have 

 not neglected a request coming from so eminent a quarter, I am bound to state that I 

 have found the subject 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 doctrine requires. 



The imperfection (due, I believe, to our imperfect acquaintance with the subject) in 

 the geological record cannot in many cases be doubted, but we have no right to make 

 capital out of unknown data. We must therefore deal with the facts as we find them, 

 and see how far they will bear upon the subject under examination. It may be quite 

 true that the strata at great distances cannot be positively asserted to be absolutely 

 contemporaneous, although they may contain some of the same animals. 



Darwin's tempting and beautiful theory of descent with modification, of which 

 Prof. Huxley is an enthusiastic supporter, is rapidly gaining adherents; 1 it bears a 

 charm that appears to be almost irresistible, and I would be the last person to assert 

 that it may not represent the actual mode of specific development, but it must likewise 

 be frankly admitted that we are at times stopped by a number of questions that seem to 

 plunge the conception into a maze of inexplicable, nay, mysterious difficulties ; nor has 

 Darwin himself, as far as I am aware; said how he supposes the first primordial form to 

 have been created. 



Tyndall observes, in his admirable Address to the Belfast Meeting of the British 

 Association, " If you ask me whether there exists the least evidence to prove that any 

 form of life can be developed out of matter, without demonstrable antecedent life, my reply 

 is that evidence, considered perfectly conclusive by many, has been adduced ; and that 

 were some of us, who have pondered this question, to follow a very common example and 

 accept testimony because it falls in with our belief, we also should eagerly close with the 

 evidence referred to. But there is in the true man of science a wish stronger than the 

 wish to have his beliefs upheld, namely, the wish to have them true ; and this stronger 

 1 " The Coming of Age of the Origin of Species," ' Nature,' May Cth, 1880. 



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