Origin of Species Variorum

→ any in the classification of animals; 1859 1860 1861 1866

all; 1869 1872

→ true, though its importance has sometimes been exaggerated. 1866

true. 1859 1860 1861 1869 1872

→ Thus 1866

Nevertheless, their importance has sometimes been exaggerated, owing to the adaptive characters of larvæ not having been excluded; in order to show this, 1872

→ the 1866

by the aid of such characters alone the 1872

→ in accordance with their embryological differences, for the sake of showing that such an arrangement is not 1866

and the arrangement did not prove 1872

→ 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

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

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

↑ 3 blocks not present in 1859 1860 1861 1866; present in 1869 1872

But there can be no doubt that characters derived from the embryo are generally of the highest value, not only with animals but with plants. Thus the two 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.

→ in the case of crustaceans, 1859 1860 1861 1866 1869

with crustaceans, any 1872

allied genera, namely Cypris and Cytherea, there is no such organ; one species of Cypridina has well-developed branchiæ, whilst another species is destitute of them.

We can see why characters derived from the embryo should be of equal importance with those derived from the adult, for

a natural

our

classifications

classification

of course

include

includes

all

ages.

ages

~~each~~

each

~~species.~~

species.

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

embryological

embryonic

characters are the most important of →any in the classification of animals; and this doctrine has very generally been admitted as →true, though its importance has sometimes been exaggerated. →Thus Fritz

Müller

~~has~~

has

arranged →the great class of

crustaceans,

crustaceans

→in accordance with their embryological differences, for the sake of showing that such an arrangement is not a natural one. →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. ↑ 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,