NOTES ON THE HISTRIOBDELLID^. 
211 
unicellular^ but may become plurinuclear by division of tlie 
original single large nucleus. The bodies above described are 
not referred to either by Foettinger or by Shearer, though 
they are distinctly shown in the figures of longitudinal 
sections by the former. They are entirely distinct from the 
salivary glands of the latter author, which also occur in 
St ratiodrilus, and lie further forwards in close relation to 
the jaws and their muscles. Their physiological connections 
may be with the nephridial and not the digestive system. 
Another conspicuous structure in this region, not repre- 
sented or not recognised in Histr iobdella, lies on the 
dorsal side of the head, a little further forward. This is a 
median organ (figs. 4 to 6 and 13, gl. d.), deeply divided 
behind into right and left lobes, which lie at the sides of the 
oesophagus, and are thus dorsal to the jaws. The unpaired 
part very closely invests the dorsal surface of the oesophagus. 
In front it becomes divided into three distinct lobes, giving 
off dorsally narrow processes, which end in the epidermal 
layer. 
The nature of this organ — the dorsal gland — is doubtful. 
Its substance stains deeply with haematoxylin, when it 
presents a vacuolated appearance, suggesting that of a gland 
for secreting mucus. It is not divided distinctly into cells, 
and contains only a few nuclei, which are very similar to 
those of the cells of the glands belonging to the anterior 
limbs. 
Yet another pair of glands which have not been noticed 
hitherto may be referred to here. These are a pair of 
spherical masses of cells (figs. 4 to 6, r. gl.), each situated at 
the side of the anus in close relation to the corresponding- 
posterior limb-gland. The cells have a generally radial 
arrangement, but I have found no lumen, and have not been 
able to trace any duct, and there is no definite evidence that 
these glands, which may be termed on account of their 
position the rectal glands, have any outlet. 
