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The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from On the Origin of Species by Charles Darwin: to Mr. Waterhouse's remark, whilst investigating this Order, and I am fully
convinced that the rule almost invariably holds good with cirripedes. I
shall, in my future work, give a list of the more remarkable cases; I will
here only briefly give one, as it illustrates the rule in its largest
application. The opercular valves of sessile cirripedes (rock barnacles)
are, in every sense of the word, very important structures, and they differ
extremely little even in different genera; but in the several species of
one genus, Pyrgoma, these valves present a marvellous amount of
diversification: the homologous valves in the different species being
sometimes wholly unlike in shape; and the amount of variation in the
individuals of several of the species is so great, that it is no
On the Origin of Species |
