THE CALCIFEROUS GLANDS OF EARTHWORMS. 
461 
free channel in the middle ; of these folds there may be about a dozen on each side 
in each segment. Neighbouring folds sometimes join and fuse at or near their free 
edges, at any rate on the dorsal and ventral regions of the oesophageal wall. Hori- 
zontal sections give evidence also of a ventral and. of a less marked dorsal fold run- 
ning longitudinally, the ventral being continuous from segment to segment ; but these 
are not so conspicuous in transverse sections as might have been expected. Alternate 
transverse folds are sometimes regularly smaller ; they might be called ridges, in 
distinction from the lamellae, with which they alternate. 
In these segments— especially well marked in xii and xiii — is to be seen a very 
striking system of transverse channels in the oesophageal wall ; these vessels are 
about twelve per segment, are broad— equal in breadth, where they are best seen, to 
the interval between successive channels — and are not united by longitudinal con- 
nections. Above they join the supra-intestinal — a specialisation of the gut plexus 
(or sinus) ; below there is no median vessel, and the transverse channels are there- 
fore continuous across the middle line. 
The epithelium of this portion of the oesophagus (fig. 2) consists of cells which 
are shortly to markedly columnar, their average height being about 25 /r, and the 
extremes about 14 to 35 /r. The protoplasm has a fibrillar structure, the fibrillse 
passing in a generally vertical direction (vertical to the surface of the cell) ; they 
frequently form a reticulum, especially near the surface, where , they are more 
numerous than in the deeper parts of the cell. There are no rodlets or cilia ; the 
surface of the cell consists of a deeper staining layer, homogeneous and compact, 
which receives and is continuous with the fibrillse in the interior of the cell. 
Cell partitions are apparently formed by vertical walls of the same nature as the 
intracellular fibrillse ; where the cells are cut tangentially to the surface of the layer 
the partitions are seen to constitute a honeycomb -like arrangement. These partitions 
are also continuous at the surface of the cells with the homogeneous surface layer. 
The rest of the cell is quite clear — as if it were merely empty spaces. The nucleus, 
often near the middle of the height of the cell, sometimes nearer the base, is round 
to roundly ovoid ; the chromatin is in the form of scattered grains, with one large 
particle which is apparently constant. 
In the middle of each lamella is an axis, also fibrillar in structure (fig. 2), and 
continuous with the fibrillse of the cells and with the partitions between the cells. 
This axis is mostly, in our preparations, not divided by a blood film in its centre, 
owing to the fact that this portion of the alimentary canal does not retain its blood 
supply after fixation ; in places, however, a satisfactory demonstration of the basal 
sinus between the epithelial and muscular coats of the oesophagus and of its extensions 
into the axis of the lamellae is obtained. Flattened nuclei may be present in the 
axis. The circular and longitudinal muscular coats are both well marked. 
Owing to the emptying of the blood spaces post-mortem in this portion of the 
tube our sections do not actually demonstrate the regular series of the transverse 
