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13 - Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Or
13-03 - Rules and difficulties in classification, explained on the theory of descent with modification
The same fact holds good with flowering plants, of which the two main divisions have been founded on characters derived from the embryo, on the number and position of the embryonic leaves or cotyledons, and on the mode of development of the plumule and radicle.
In our discussion on embryology, we shall see why such characters are so valuable, on the view of classification tacitly including the idea of descent.
Our classifications are often plainly influenced by chains of affinities.
Nothing can be easier than to define a number of characters common to all birds; but in the case of crustaceans, such definition has hitherto been found impossible.
There are crustaceans at the opposite ends of the series, which have hardly a character in common; yet the species at both ends, from being plainly allied to others, and these to others, and so onwards, can be recognised as unequivocally belonging to this, and to no other class of the Articulata.
12 - Geographical Distribution -- continued
12-50 - On colonisation from the nearest source with subsequent modification
I can hardly doubt that this rule is generally true, though it would be difficult to prove it.
Amongst mammals, we see it strikingly displayed in Bats, and in a lesser degree in the Felidae and Canidae.
We see it, if we compare the distribution of butterflies and beetles.