Studies on Earthworms. - Journal of Cell Science

250 WILLIAM BLAXLAM) BENHAM.
somites, xix and xs; whilst behind this comes the sacculated,
typhlosolar region, with thin walls covered externally by the
large, yellow coslomie epithelium; in this form the typhlosole
is well developed, and, as usual, presents a blood-vessel in
frequent connection with the dorsal trunk.
In other forms the tubular portion has a greater extent; for
instance, in Anteus it extends from about somite vm to xvin,
in Titanus from somite vi to xv. In Acanthodrilus,
judging by Perrier's figures, one species has none, in another
this region extends to somite xx, and in Urochseta as far as
somite xv. In all cases where a structure is said to extend to
a certain somite, it is understood to exist in that somite as well
as in the preceding somites.
In these forms ossophageal glands are absent, but their analogue
seems to be frequently present in the form of one or more
pairs of glands, which contain carbonate of lime, situated on
the tubular region of the intestine.
In Urochseta there are three pairs of such glands, elongated
and ovoid, in somites vm, ix, x; in Plutellus three
pairs of glands of the same nature occur in somites x, xi, xu,
but are reniform.
In Titanus is a single pair of white, nearly spherical glands,
in somite xnr, which Perrier mistook for a part of the vascular
system. He describes it as a " ventricle." I have had the
good fortune of dissecting a Titanus, and have seen distinctly
the large openings of these glands into the intestine.
One of the characteristics of the genus Perichseta appears
to be the presence of a pair of elongated caeca, springing
from the ventral surface of the sacculated intestine in somite
xxvi or xxvn. In P. Sieboldii, Horst, there are six pairs of
coeca in somite xxvi. Although Perionyx resembles Perich
set a in many points these caeca are absent in it.
The typhlosole is usually a sub-cylindrical longitudinal
valve produced by an involution along the dorsal wall of the
sacculated intestine; but in Titanus this organ is flattened
from side to side, whilst in Pontodrilus the vessel alone
exists. Pie urochseta has no typhlosole and possesses a