4
BRITISH WELL-WORMS.
Beddard prepared his Monograph he remarked that "the number
of species of this genus is at least four ; and they are all well
characterized." This is a great gain. So clearly defined are
the different species that, by means of the setae alone we can
determine at once under which head a given specimen should
fall, and consequently can with equal ease determine whether or
not a worm submitted for examination has been already
described.
The first of the species to be described, if we follow Mr.
Beddard's arrangement, was Phreoryctes menkeanus, Hoffm. The
number of segments exceeds five hundred, the setae are in four
single rows, and the ventral setae exceed the dorsal in length.
Leydig, Vejdovsky, Giard, Timm, and others have written on
this species.
Next in chronological order comes Ph. filiformis, Clap.,
which is about a quarter the length of its predecessor, and has
the dorsal setae longer than the ventral. The seta1, moreover,
are shorter and much more hooked. Beddard calls attention to
the difference of opinion which has prevailed among authors
respecting these two species. He admits their possible identity,
but emphasizes the fact that their length is widely different.
Michaelsen seems disposed at present to place all the species
under one. Ph. menkeanus was described in 1843, Ph. filiformis in
1862.
Beddard added a third species in 1888 under the title Ph.
smithii. This species comes from New Zealand, is a compara-
tively stout worm, has its setae paired—which is the case in no
other species—the dorsal setae being longer than the ventral in
the hinder segments. "The shaft of the setae which is implanted
in the body wall is curved, not straight as in the other species."
It may be added that the worm was collected by Mr. W. W.
Smith, "chiefly in fresh pools, where it lives in association with
a species of Limnodrilus ; one example was discovered in marshy
soil ; so that this species is equally at home in water and in damp
soil."
The remaining species belongs to North America. It was
described in 1890 by Mr. Forbes and bears the name Ph.
emissarius. It is readily distinguishable from the rest by reason
of the total disappearance of the dorsal setae from four-fifths of
the segments. The worm is six or eight inches in length, is
composed of nearly 400 segments, very thin. The setae are