two lines in breadth, with twenty-five body-segments, and without
projecting setigerous tubercles or jointed cirri. The small cephalic
lobe bore four eyes and five tentacles; each body-segment had on each
side at the margin a tuft of simple setae directed obliquely upwards,
and at some distance from this, upon the ventral surface, a group of
thicker setae with a strongly uncinate bidentate apex. There was above
EACH of the lateral tufts of bristles a branchia, simple on a few of the
foremost segments, and then strongly arborescent to the end of the body.
The animal, a female filled with ova, evidently, from these characters,
belongs to the family of the Amphinomidae; the only family the members
of which, being excellent swimmers, live in the open sea.

That this animal had not strayed accidentally into the Lepas, but
appertained to it as a regular and permanent guest, is evidenced by its
considerable size in proportion to the narrow entrance of the test of
the Lepas, by the complete absence of the iridescence which usually
distinguishes the skin of free Annelides and especially of the
Amphinomidae, by the formation and position of the inferior setae, etc.
But that a worm belonging to this particular family Amphinomidae living
in the high sea, occurs as a guest in the Lepas, which also floats in
the sea attached to wood, etc., is at once intelligible from the
stand-point of the Darwinian theory, whilst the relationship of this
parasite to the free-living worms of the open sea remains perfectly
unintelligible under the supposition that it was independently created
for dwelling in the Lepas.

But however favourable the examples hitherto referred to may be for
Darwin, the objection may be raised against them, and that with perfect
justice, that they are only isolated facts, which, when the
considerations founded upon them are carried far beyond what is