ANNELIDA. 
595 
III. Platyelminthes : > 
Trematoda; Hirudinea; Onycliophora ; Cestoidea; Dendro- 
coela ; Rhabdocoela. 
Ehlers, on the other hand, divides Vermes into these eight 
classes'^ : — 
I. Cestoda, Rud. 
II. Acanthocephala, Rud. 
III. Trematoda, Rud. 
IV. Turbellaria, E^r^r^.s. str. 
The Annelida he resolves into 
V. Schultze, 
VI. Nematoda, Rud. 
VII. Gephyrea, Qtrfgs. 
VIII. Annelida, Sav. 
two subclasses — Cheetopoda 
and Discophora. The Cheetopoda include four orders — Nereidea, 
Ariciea, Serpulea, and Lumbricina. The first three of these cor- 
respond collectively to the order Polycheeta of Grube, which is 
equivalent to the class Annelida of De Quatrefages. 
Grude [op. cit. pp. 77-93) enumerates more than a liundred 
species of Annelids from the fauna of Lossini. These, with 
the exception of eight, all belong to the order Polycheeta. Ihe 
new forms, including two genera, have already been described 
by the author in a memoir communicated to TroscheTs Archiv 
for 1863. 
POLYCHA3TA. 
The essays of De Quatrefages, Kdlliker, and Claparede, cited 
in the above list, refer exclusively to the Annelids of this 
order. 
According to De Quatrefages, the principal genera, and even 
subgenera, of these Annelids are very cosmopolitan in their 
distribution ; so that they do not restrict themselves to definite 
zoological regions, as do other groups of the animal kingdom. 
The species, however, are much more limited in their range, 
those of the same genus being often different even in con- 
tiguous stations. Not one species, according to De Quatre- 
fages, is common to the shores of the Bay of Biscay and the 
Mediterranean. Seldom is the same species common to two 
continents, to two hemispheres, to the eastern and western seas 
of the same continent, &c. The few exceptions to this rule 
may readily be accounted for by the action of ocean-currents. 
In our study of the Annelida most remarkable for their pecu- 
liarities of organization, the grouping of the species into 
separate faunae is best seen. It cannot be said that notable 
differences in complexity of structure, corresponding to those 
observed by Milne-Edwards among the Crustacea, mark the 
Annelida obtained from different latitudes. Lastly, the distri- 
bution of these animals is much influenced by the character of 
the coast — granitic and schistose coasts being most rich, while 
calcareous coasts are comparatively poor in Annelids. 
2 Q 2 
