185
BRITISH ANNELIDS.
WITH ESPECIAL REFERENCE TO THE EARTHWORMS OF ESSEX.
By REV. HILDERIC FRIEND, F.L.S.
(Continued from page 174.)
ALTHOUGH Eisen discovered an example of a worm which lived
among decaying timber upwards of twenty years ago, and named
it the "Tree-haunter" (Dendrobaena), yet the species or group was
never studied in a consecutive and exhaustive manner, either at
home or abroad, until I took it up two years ago, and published my
results in the "Journal of the Linnean Society" for 1892 (Zoology,
vol. xxiv., pp. 292 seq.). Since that sketch was written, I have been
able to extend my researches and add more than one fact of very
great biological interest and importance to those already known. My
present paper will be limited to a notice of this third group of worms
belonging to the genus Allolobophora.
Allolobophora : §3, Dendrobaena.
The worms belonging to this group are of two kinds. They can
(with some exceptions, perhaps) live either in the soil or in the
timber of decaying trees. Their habitat materially affects their size,
colour, shape, and appearance. So much is this the case that it is
in some instances almost impossible to decide whether the terrestrial
species is the same as the dendrobaenic or not. This is a point of
extreme interest, as we have here a means of studying, in careful
detail, the effect of environment on species, and the possible ultimate
development of species from varieties. The varieties which frequent
trees are invariably of a warm brown colour on the back, with the
girdle and under surface lighter. They seldom exceed one and a-half
inches in length, and have an octangular-shaped tail, due to the wide
disposition of the setae, which are in eight almost equidistant rows.
The prostomium may not cut the peristomium at all, or it may perfectly
bisect it. The girdle occupies from five to eight segments, com-
mencing somewhere between the 24th and 31st. The male or
spermiducal pores are on segment 15, usually with prominent
papillae, which in one case extend over the two adjoining segments.
The clitellar papillae (tubercula pubertatis) are either absent, or occur
on two or three consecutive, never on alternate, segments. The first
dorsal pore is usually between the 5th and 6th segments. I have
found spermatophores only on the terrestrial forms of two species.
O