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from au ancieut period very slightly modified ought, I think, to be 

 omitted; and those fonns alone considered which have undergone 

 considerable change at each successive epoch. My fear is whether 

 the Brachiopods have changed enough. The absolute amount of 

 difFei-ence of the forms in such groups at the opposite extremes of 

 times 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 secui to think, because it has transmitted to the present 

 daj- 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 iuiportant essay (far more important 

 than a hundred literary reviews), might be written by one like 

 youi'self, and without very gi-eat labour," &c. In several subse- 

 quently written letters, Darwin reiterated his suggestion. He could 

 assure them that he had not neglected a request coming from so 

 eminent a quarter; but he was bound to state that he had found 

 the subject beset with so manj'- apparently inexplicable difiiculties, 

 that year after year had passed away without his being able to 

 trace the descent With modification among the Brachiopoda which 

 the Darwinian Doctrine required. The impei'fection (one due, he 

 believed to our slight acquaintance with the subject) in the geolo- 

 gical record could not in many cases be doubted, but we had no 

 right to make capital out of unknown data, we must therefore deal 

 with facts as we found them, and see how far they would bear upon 

 the subject under examination. It was quite true that strata at 

 great distances could not be positively asserted to be, strictly speak- 

 ing, absolutely contemporaneous, although they might contain the 

 same animal remains. It was very probable that some species 

 might have emigrated from the sea bottom on which they oi-iginally 

 lived to some more favourable locality, and become to some extent 

 modified. No one could seriously doubt that life had continued to 

 be represented under one form or another ever since it was first 

 brought into existence. He consequently could not agree with 

 Deshayes and others who believed in a total extinction of the 

 animal creation at certain specified periods. Notwithstanding the 

 theoretical doctrine that had been promulgated with respect to the 

 origin of species, we were still, and would probably for ever remain, 

 in the dark, or within the region of suppositions with respect to so 



