11 



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, PI. II.) 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.l, figs. 3 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.l, 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 matitle edges are 

 prolonged outwards to form the siphons. In the full grown 

 animal these have a maximum length, when extended, of 

 about 1 cm. In the young cockle their length is relatively 

 much greater. 



