57 
Mr. Carrutliers, wlio is at the head of the botanical department of 
the British Mnsenm, and considered one of the most distin¬ 
guished and able botanists in Europe. M. Barrande, in alluding 
to Mr. Davidson, states that that eminent geologist published 
in the “ Geological Magazine ” a paper entitled, “ What is a 
Bracliiopod ? ” which exposes in the most succinct and most 
clear manner the results of all the laboims and discoveries 
relative to the Brachiopods, results to which Mr. Davidson has 
contributed incomparably more than any other investigator. 
Mr. Davidson is also the author of the very extensive and 
exhaustive work on Brachiopoda, now in the course of publica¬ 
tion by the Palinontographical Society. M. Barrande quotes 
largely from Mr. Davidson’s three papers in the “ Geological 
Ma gazine ” for 1877. We shall here merely epitomize some 
of the latter’s opinions and the conclusions at which he has 
arrived. At page 271 he says, “ Darwin’s tempting and beau¬ 
tiful theory of descent with modification 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. We are stopped by a number of questions that 
seem to plunge the conception in a maze of inexplicable, nay, 
mysterious difficulties ; nor has Darwin, as far as I am aware, 
said how he supposes the first primordial form to have been 
introduced. The theory is, at best, as far as we can at present 
perceive with our imperfect state of knowledge, but half the 
truth, being well enough in many cases as between species and 
species ; for it is evident that many so termed species may be 
nothing more than modifications produced by descent. It 
applies likewise to accidental variations as between closely 
allied genera ; yet there is much more than this, with respect 
to which the theory seems insufficient. The strange geological 
persistency of certain types, such as Lingula, Discina, Nautilus, 
&c., seems also to bar the at present thorough acceptance of 
such a theory of general descent with modification.” He further 
states that “We have no positive evidence of those modifica¬ 
tions which the theory involves, for types on the whole appear 
permanent as long as they continue, and when a genus disap¬ 
pears there is no modification, that I can see, of any of the 
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