| → all; 1869 1872 |
| any in the classification of animals; 1859 1860 1861 1866 |
|
| → true. 1859 1860 1861 1869 1872 |
| true, though its importance has sometimes been exaggerated. 1866 |
|
| ↑ 1 blocks not present in 1859 1860 1861 1869; present in 1866 1872 |
| Thus
Fritz Müller
has
arranged the
great class of crustaceans
in accordance with their embryological differences, for the sake of showing that such an arrangement is not
a natural one.
|
|
| → Nevertheless their importance has sometimes been exaggerated; in order to show this, Fritz Müller arranged by the aid of such characters the great class of crustaceans, and the arrangement did not prove a natural one. 1869 |
| 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 em- bryonic leaves or cotyledons, and on the mode of development of the plumule and radicle. 1859 1860 1861 |
| The general fact of the importance of embryological characters holds good with flowering plants, of which the two main divisions have been founded on differences in the embryo,— on the number and position of the cotyledons, and on the mode of development of the plumule and radicle. 1866 |
|
| → characters derived from the embryo are generally 1869 |
| embryonic, excluding larval characters, are 1872 |
|
| → not 1869 |
| for classification, not 1872 |
|
| → in the case of crustaceans, 1859 1860 1861 1866 1869 |
| with crustaceans, any 1872 |
|
|
But it is by no means obvious, on the ordinary view, why the structure of the embryo should be more important for this purpose than that of the adult, which alone plays its full part in the economy of nature. Yet it has been strongly urged by those great naturalists, Milne Edwards and Agassiz, that
characters are the most important of
→all;
and this doctrine has very generally been admitted as
→true.
↑ →Nevertheless their importance has sometimes been exaggerated; in order to show this, Fritz Müller arranged by the aid of such characters the great class of crustaceans, and the arrangement did not prove a natural one. But there can be no doubt that
→characters derived from the embryo are generally
of the highest
→not
only with animals but with plants. Thus the
main divisions of flowering plants are founded on differences in the embryo,— on the number and position of the cotyledons, and on the mode of development of the plumule and radicle. We shall immediately see why these characters possess so high a value in classification, namely, from the natural system being genealogical in its arrangement.
|
|
| 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. |
|
| Geographical distribution has often been used, though perhaps not quite logically, in classification, more especially in very large groups of closely allied forms.
|
