THE CALCIFEROUS GLANDS OF EARTHWORMS. 
477 
In segment xii the whole circumference of the oesophagus becomes surrounded by 
tunnels, which are, however, lower in the dorsal and ventral regions than elsewhere ; 
there are about 50 in the half circumference. The disintegration of the epithelium 
is, in one of the specimens here described, though not in another, much less than 
in the preceding segment ; the epithelium is approximately cubical, and there are 
no cilia, and no granules are being discharged. 
The tunnels continue through segment xiii, where they are lower. Their 
epithelium is low, and not disintegrating. The oesophageal epithelium is now 
longitudinally folded again in a regular manner. Rodlets are present as far as xiii, 
but are absent in xiv. The tunnels die away in xiv. 
The vascular relations of the gland are similar to those jn Helodrilus. 
A notable feature was the occurrence of numerous groups of “ chromophil cells,” 
of the same kind as those of the pharyngeal glands, on the oesophagus throughout 
segments ix and x. 
Criticisms of Previous Work. 
The papers which will be referred to in what follows are those by Harrington 
(12), Ribaucourt (21), and Combault (6, 7, 8). The latter author has a number 
of other papers, which, however, are largely physiological, and in part concerned 
with the circulation through the glands; his paper of 1909 (8) is to some extent 
a summing up of his results, and repeats much of his earlier communications. 
A word on the position of the glands to begin with : Ribaucourt nowhere 
mentions their situation ; Combault invariably places them one segment behind 
their proper position — the first pair of swellings, the oesophageal pouches, in xi, 
whereas they are in x. 
It has been shown above that the glands ( i.e . the tunnels) and the oesophageal 
lining membrane together constitute the epithelial layer, and (except the blood, 
which bathes the bases of the cells) no other constituent of the wall is present from 
the lumen of the gut outwards as far as the so-called external sinus. Combault 
therefore mistakes the constitution of this part of the tube when he writes of the 
glands as “ un veritable manchon oesophagien . . . creus6 dans le tissu conjonctif 
qui s6pare l’epith^lium oesophagien de la couche musculaire,” or of “ une couche de 
tissu conjonctif fasciculi ou sont loges les sinus internes ” (i.e. the dilated inner ends 
of the sinuses in the lamellae) ; in this tissue one is supposed frequently to meet with 
muscular fibres. On what we believe to be the true view of the morphology of the 
glands there is no place for either muscular or fibrous tissue in this situation. 
Before mentioning Harrington’s view of the origin of the glandular epithelium, 
it is necessary to allude to the process of secretion as described by him. The cells 
of the glandular layer are irregular, and give an irregular appearance to the layer. 
After an active wave of secretion the cell projections may almost entirely disappear, 
being levelled by disintegration to the general surface. The cells form a syncytium, 
