AN ICHTHYOBDELLID PARASITIC ON SAND WHITING. 11 
the sucker wall, and, measuring about 20 /u in diameter, are 
about half the size of the same glands in the posterior sucker. 
Among them are placed the smaller mucous glands, and both 
types of glands open by ducts on the concave surface of the 
sucker. In the posterior sucker these glands are distributed 
over the whole sucker. The mucous glands are found also 
forming a pharyngeal group with ducts opening into the 
pharynx, and they extend posteriorly and lie among the 
salivary glands but nearer the body wall ; they are not 
present below the glandular oesophageal pouches. 
Clitellar Glands. 
As has been remarked by various authors, the development 
of the unicellular glands in the Ichthyobdellids is most 
remarkable. To quote Bourne (1884): “They attain rela- 
tively, and in Pontobdella and Branchellion actually, 
huge dimensions.” 
In this leech the largest among these cells have a diameter 
of 170 /u, and, if they are situated far back in the body, a duct 
7 or 8 mm. long. The clitellar glands extend in the body 
region from the posterior sucker to the beginning of the 
clitellum. 
They are placed inside the body wall musculature and 
occupy practically all the space between it and the alimentary, 
reproductive, and lacuna systems. Text-fig. 3, drawn from a 
transverse section through the region of the thick-walled 
middle gut, shows the degree of development of these glands 
(Cl. gl. 1, Cl. gl. 2). 
Their ducts open all round the clitellum, that is from the 
level of the 10th nerve ganglion to midway between the 
12th-13th nerve ganglia. SukatschofPs (1912) excellent 
work on these glands showed that in Branchellion there 
were three types producing different secretions, and he gives 
a description of extraordinary development of the branched 
nucleus, which may come to measure 336 ju and which he 
compares (p. 488) with other examples of nuclei of this type 
in the animal kingdom. 
