e fact of great significance, which seems more than any other to
render it highly improbable that we shall ever find air-breathers of
the highest class in any of the Primary strata, or in any of the older
members of the Secondary series.") I rather demur to your argument from
Cetacea: as they are such greatly modified mammals, they ought to have
come in rather later in the series. You will think me rather impudent,
but the discussion at the end of Chapter IX. on man (192/4. Loc. cit.,
pages 167-73, "Introduction of Man, to what extent a Change of the
System."), who thinks so much of his fine self, seems to me too long, or
rather superfluous, and too orthodox, except for the beneficed clergy.

LETTER 193. TO V. CARUS.

(193/1. The following letter refers to the 4th edition of the "Origin,"
1866, which was translated by Professor Carus, and formed the 3rd German
edition. Carus continued to translate Darwin's books, and a strong
bond of friendship grew up between author and translator (see "Life and
Letters," III., page 48). Nageli's pamphlet was first noticed in the 5th
English edition.)

Down, November 21st, 1866.

...With respect to a note on Nageli (193/2. "Entstehung und Begriff der
Naturhistorischen Art," an Address given before the Royal Academy of
Sciences at Munich, March 28th, 1865. See "Life and Letters," III.,
page 50, for Mr. Darwin's letter to the late Prof. Nageli.) I find on
consideration it would be too long; for so good a pamphlet ought to be
discussed at full length or not at all. He makes a mistake in supposing
that I say that useful characters are always constant. His view about
distinct species converging and acquiring the same identical structure
is by implication answered in the discussion which I have given on the
endless diversity of means for gaining the same end.

The most important point, as it seems to me, in the pamphlet is that on
the morphological characters of plants, and I find I could not answer
this without going into much detail.

The answer would be, as it seems to me, that important morphological
characters, such as the position of the ovules and the relative position
of the stamens to the ovarium (hypogynous, perigynous, etc.) are
sometimes variable in the same species, as I incidentally mention when
treating of the ray-florets in the Compositae and Umbelliferae; and I
do not see how Nageli could maintain that differences in such characters
prove an inherent tendency towards