32
BRITISH ANNELIDS.
Until last year the story of the Square-tail had never been fully
told by any English author. I had the honour, however, of giving a
lengthy sketch of its history in "Science Gossip," 1891, p. 80, and
must refer the reader to that periodical for illustrations and details.
When I speak of Allurus as the Square-tail, I wish it to be under-
stood that the term is to be used in a modified sense, as we have
one or two other worms which sometimes present this peculiarity,
only in a less marked degree. I am anxious, however, as far as
possible to attach to each species of worm a popular name which
will pretty accurately set forth its characteristic feature, so that it
may be possible to speak of each worm without being compelled
always to adopt the technical name of the species. Now it was on
account of the shape of the posterior half of this worm that it was
named Allurus (Greek alios, another, different, and oura, tail or
hinderpart), when it was separated from the old genus Lumbricus,
and made the type of a new species.
Savigny is the first author who gives us any information respect-
ing Allurus, which he named Enterion tetraedrum. This was in
1828, in which year Duges also wrote about it, and named it Amphis-
baena, because, like the serpent of which Lucanus sang, it could go
backwards as readily as forwards. In 1837, Duges regarded the two
worms as distinct, and called Savigny's species Lumbricus tetraedrus,
and his own Lumbricus amphisbaena. The distinctions which he
points out have been overlooked by later writers until Eisen took up
the subject, and now we find two or three well-marked varieties whose
further study is likely to yield some interesting results.
In 1843 Hoffmeister gave our worm a new name, calling it the
Agile-worm (Lumbricus agilis); but though the distinction is a good
one when the square tail and the green worm, for example, are con-
trasted, it does not hold good when the purple worm (Lumbricus
purpureus) and some others are placed in competition with it. Eisen
was the first to recognise its generic distinctness from Lumbricus,
and in 1870 gave it the name which it still continues to bear. Now
that it has come of age, and had its biography written, I hope no one
will venture to alter its name, and so add to the confusing list of
synonyms by which it is already obscured.
Allurus ranges from one to two inches in length, but I have taken
it frequently in its adult stage under an inch long. It is the smallest
species we possess, and may easily be overlooked, not only by reason
of its diminutive size, but also on account of its protective coloura-