BRITISH WELL-WORMS.
3
the earthworms they are usually in pairs. In some species the
perfect seta has an imperfect one by its side, and the seta of the
dorsal portion of the body usually vary from those of the ventral.
Even in the species which has the normal arrangement of the
setae we still find a difference in size between the dorsal and
ventral pairs. Several biologists have pointed out the existence
here, as among the Enchytraeids, of a peculiar appendage to
the ventral nerve cord in each segment. Normally there are
two pairs of testes in segments ten and eleven, and two pairs of
ovaries in the twelfth and thirteenth segments, as was first
clearly indicated by Mr. F. E. Beddard. There are two or three
pairs of Spermathecae in the species already described. The
prostomium is generally divided by a constriction. Mr. Beddard
has described a closely related genus under the name of Pelodrilus
the two genera being placed together under the Family
Phreoryctidae. He gives the following definition of the
Family :—
" Definition.—Aquatic or terrestrial Oligochaeta of slender form,
often exceedingly long. Setae in four rows of single setae or paired,
sigmoid. Testes in X., XI. Ovaries in XII., XIII. or XIII. only,
Sperm-ducts, two pairs opening separately, without spermiducal glands,
Spermathecae in front of testes, without diverticula. No genital setae."
In one or two particulars this definition will now require
modification. In regard to the setae we shall have to read in
future—"Setas in two or four rows," and some qualification of
the phrase about genital setae must be introduced. Mr. Beddard
next proceeds to define the genus Phreoryctes. First we have the
synonyms as follows :—
Phreoryctes, Hoffmeister.
Haplotaxis, Hoffmeister.
Nemodrilus, Claparede.
Georyctes, Schlotthauber.
According to Dr. Michaelsen, whom I shall quote later, this
synonymy is incomplete.
" Definition.—Setae in four rows of single setae or pairs.
Clitellum XL—XIV. Prostomium divided by a transverse constric-
tion. Testes in X, XI. Ovaries in XII., XIII. Vasa deferentia open
separately on to XI. and XII. ; oviducts on to border line between seg-
ments XII/XIII. and XIII/XIV. Spermathecae, two or three pairs in
VII., VIII. (IX.)."
Here again the same modification applies to the setae. We
now come to a consideration of the known species. When Mr.