pation of the
division by Leuckart in 1839 of the Radiata of Cuvier into
Coelenterata and Echinodermata.

The "Polypes" of Lamarck included not only the forms now known as such,
but also the Rotifera and Protozoa, though, as we shall see, he
afterwards in his course of 1807 eliminated from this heterogeneous
assemblage the Infusoria.

Comparing this classification with that of Cuvier[121] published in
1798, we find that in the most important respects, _i.e._, the
foundation of the classes of Crustacea, Arachnida, and Radiata, there is
a great advance over Cuvier's system. In Cuvier's work the molluscs are
separated from the worms, and they are divided into three groups,
Cephalopodes, Gasteropodes, and Acephales--an arrangement which still
holds, that of Lamarck into Mollusques cephales and Mollusques acephales
being much less natural. With the elimination of the Mollusca, Cuvier
allowed the Vers or Vermes of Linne to remain undisturbed, except that
the Zooephytes, the equivalent of Lamarck's Polypes, are separately
treated.

He agrees with Cuvier in placing the molluscs at the head of the
invertebrates, a course still pursued by some zooelogists at the present
day. He states in the _Philosophie Zoologique_[122] that in his course
of lectures of the year 1799 he established the class of Crustacea, and
adds that "although this class is essentially distinct, it was not until
six or seven years after that some naturalists consented to adopt it."
The year following, or in his course of 1800, he separated from the
insects the class of Arachnida, as "easy and necessary to be
distinguished." But in 1809 he says that this class "is not yet admitted
into any other work than my own."[123] As to the class of Annelides, he
remarks: "Cuvier having discovered the existence of arterial and venous
vessels in different animals which have been confounded under the name
of worms (_Vers_) with other animals very differently organized, I
immediately employed the consideration of this new fact in rendering my
classification more perfect, and in my course of the year 10 (1802) I
established the class of Annelides, a class which I have placed after
the molluscs and before the crustaceans, as their known organization
requires." He first established this class in his _Recherches sur les
corps vivans_ (1802), but it was several years before it was adopted by
naturalists.

The next work in which Lamarck deals with the classification of the
in