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188 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
with deep grooves parallel to the anterior margins, and are 
ciliated. The other surfaces are smooth and non-ciliated. 
Cilia are present on all surfaces of the grooves and ridges. 
Each ridge is roughly quadrangular in section (fig. 24). 
The outer faces and the faces turned towards the apices 
of the palps are covered with long columnar cells bearing 
long cilia, and having abundant eosinophilous cells. The 
rest of the surface of the ridges and furrows is covered 
with cubical cells, carrying shorter cilia. The smooth 
surfaces of the palps have an epidermis of flat, almost 
squamous cells. Within the palp there is a very loose 
connective tissue, rather denser in the interior of the 
ridges and containing blood corpuscles in its interspaces. 
The mantle lobe of each side (Mn., fig. 4, Pl. IL.) is 
inserted into the extreme dorsal margin of the body, and 
round the lower margin of each adductor; anteriorly the 
right and left lobes fuse together at the dorsal surface of 
the anterior adductor. Posteriorly there are two fusions ; 
dorsal to the posterior adductor the mantle roofs in a 
portion of the mantle cavity which passes upwards over the 
adductor (Mc.1, figs. 8 and 6), and in which the terminal 
portion of the rectum and the anus lie. The first fusion 
forms the septum between the dorsal and ventral siphons. 
It is prolonged inwards from the mantle edge forming 
a horizontal shelf (Mn.1, fig. 3), which separates the 
cavity of the dorsal siphon (Mc.2, figs. 3 and 6) from the 
general mantle cavity (Mc.3, figs. 3 and 6). The second 
fusion forms the lower wall of the ventral siphon. Between 
the posterior margin of the mantle and fusion one, and 
between the first and second fusions, the mantle edges are 
prolonged outwards to form the siphons. In the full grown 
animal these have a maximum length, when extended, of 
about lcm. In the young cockle their length is relatively 
much greater. Seis 
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