BRITISH WELL-WORMS,
5
implanted singly, in four rows for about 70 segments in front, and
two ventral rows behind. This fact is peculiarly interesting in
its bearing on the specimen from Chelmsford.
§ Significance of the foregoing facts.
It is important that we should understand the force of the
facts which are gleaned by a study of the genus. To begin with
the head. When I studied the Essex specimen one of the first
things which struck me was the anomaly which presented itself
here. Three of the known species of Phreoryctes have the prosto-
mium or head segment divided into halves by a cross furrow
at about the middle ot its length ; and the prostomium is rather
elongated. This is a peculiar character, met with elsewhere,
however, though not among the true Oligochaeta. The setae are
instructive. Here, it is true, we meet with the utmost possible
diversity. Mr. Beddard, who has let few things escape him,
remarks that "the commencement of a diversity in the form of
the setae is seen in Phreoryctes, where some of the setae are longer
than the others, the dorsal longer than the ventral, or vice versa,
or the posterior longer than the anterior." Moreover, while they
are usually of the typical Lumbricid pattern, viz., sigmoid or
f shaped, and not cleft at the extremity, in one species the
shaft is straight, in another they are varied on the girdle seg-
ments, and in two cases the dorsal setae are either partially or
entirely wanting. These are significant modifications. All
departures from the type suggest one or two things, either they
imply degeneracy or adaptation and progress. This genus is
undoubtedly one of an advanced type in many ways.
I have shewn that the first name which Hoffmeister applied
to the genus was Haplotaxis, Was the name chosen to set forth
any genuine peculiarity, or was it merely haphazard ? It was
suggestive. It is the rule that aquatic annelids possess a
longitudinal muscular layer composed of "flat flakes or lamellae
imbedded in a granular substance." This layer is absent from
Phreoryctes—a fact which struck me when I examined the Essex
worm, and one which I find I have recorded in my drawings
made at the time when the worm was first placed in my hands.
It was, doubtless, this fact which led Hoffmeister to give the
name Haplotaxis to the genus. If we turn to the question of
brain structure, we find that in Phreoryctes this organ has
"the simple, bilobed character that is characteristic of the higher
Oligochaeta to which this worm is related." (Beddard, Mono-