THE CALCIFEROUS GLANDS OF EARTHWORMS. 
475 
triangular as in the adult H. caliginosus, and are always sharply bounded by a 
basement membrane. 
Towards the end of segment xiii there are appearances suggesting the opening of 
one or a few tunnels into the crypts between the folds of the oesophageal epithelium ; 
but no actual opening could be demonstrated satisfactorily. 
The Glands in the Genus Lumbricus. 
It has happened that the structure of the glands was by no means so easy to 
make out in the specimens of Lumbricus at our disposal as in those of Helodrilus 
caliginosus and H. parvus. This is partly due to the damage caused by calcareous 
concretions in the case of Lumbricus ; the glands seem to have been functioning 
actively, and the oesophageal pouches in particular were much torn in the sections 
of Lumbricus when they came to be examined. The swellings of the oesophagus 
were more marked in Liumbricus, and consequently overlapped from segment to 
segment, rendering the appearances at first sight rather confusing. The diagram- 
matic clearness with which the structures were displayed in the case of many or 
most of our specimens of Helodrilus , and the freedom from damage by calcareous 
particles, has rendered our description of them easy, and it is hoped satisfactory. 
In Lumbricus the condition is essentially the same as in Helodrilus. In segment 
x are a pair of subspherical sacs, the oesophageal pouches ; in xi are seen a pair 
of lateral swellings, with somewhat the appearance of stout sausages, applied by 
their inner curved surfaces to the sides of the alimentary tube ; in xii are a similar 
pair of swellings, of equal size with those in xi ; the section of the tube in xiii is 
somewhat dilated, and subspherical in form, the swelling being general ; in xiv 
the oesophagus is narrower, but at the hinder end of the segment it may widen 
to form the beginning of the crop. The wall of the oesophagus is longitudinally 
striated by blood channels in segments xi— xiii. 
Microscopically, the epithelial lining of the oesophagus is irregularly ridged 
and folded in segment ix, in front of the pouches ; the ridges become regular and 
longitudinal in direction as the tube passes through septum 9/10. There is one 
considerable difference between the pouches of segment x in Helodrilus and 
Ljumbricus ; — the openings of the pouches into the oesophageal tube are at a much 
more posterior level in Lumbricus ; instead of opening into the oesophagus by 
a wide mouth in segment x, the pouches communicate with the oesophageal lumen 
in the anterior part of segment xi (text-fig. l), and hence throughout segment x 
they appear in sections on each side as separate sacs. 
Longitudinal lamellae are present within the pouches over their whole circum- 
ference ; they are larger on the mesial wall of the pouch, where they extend into 
its interior so as to take up more than half the transverse diameter of the pouch. 
The union of the lamellae to form tunnels takes place, however, only on the outer 
wall. When this happens, the lamellae unite, each with its neighbours, at about 
