Origin of Species Variorum

→ in combination, 1872

correlated with others, 1859 1860 1861 1866 1869

→ 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

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

Thus 1866

→ by the aid of such characters alone the 1872

the 1866

→ and the arrangement did not prove 1872

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

↑ 1 blocks not present in 1872; present in 1866 1859 1860 1861 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.

→ embryonic, excluding larval characters, are 1872

characters derived from the embryo are generally 1869

→ for classification, not 1872

not 1869

→ with crustaceans, any 1872

in the case of crustaceans, 1859 1860 1861 1866 1869

If they find a character nearly uniform, and common to a great number of forms, and not common to others, they use it as one of high value; if common to some lesser number, they use it as of subordinate value. This principle has been broadly confessed by some naturalists to be the true one; and by none more clearly than by that excellent botanist, Aug. St. Hilaire. If

certain

several trifling

characters are always found →in combination, though no apparent bond of

connexion

connection

can be discovered between them, especial value is set on them. As in most groups of animals, important organs, such as those for propelling the blood, or for

aërating

aerating

it, or those for propagating the race, are found nearly uniform, they are considered as highly serviceable in classification; but in some groups

of animals

....

all these, the most important vital organs, are found to offer characters of quite subordinate value. Thus, as Fritz

Müller

has lately remarked, in the same group of crustaceans, Cypridina is furnished with a heart, whilst in

two

too

closely 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

our

a natural

classifications

classification

of course

include

includes

all

ages

each

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

embryonic

embryological

characters are the most important of →all; and this doctrine has very generally been admitted as →true. →Nevertheless, their importance has sometimes been exaggerated, owing to the adaptive characters of larvæ not having been excluded; in order to show this, Fritz

Müller

has

....

arranged →by the aid of such characters alone the great class of

crustaceans

crustaceans,

→and the arrangement did not prove a natural one. ↑ But there can be no doubt that →embryonic, excluding larval characters, are of the highest

value,

value

→for classification, 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.

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 →with crustaceans, any such