SEA-FISHERIES LABORATORY, 191 
and isolated fibres which terminate in the inner mantle 
fold. 
Within the mantle there is, at the margin, a filling tissue 
composed of fine connective tissue fibres, in which run the 
muscle bundles and the trunks and finer branches of the 
pallial nerve plexus; passing inwards, this begins to 
include large irregular communicating spaces, and is soon - 
reduced to a mere lining to the epidermal surfaces from 
which trabecule pass inward, forming a very coarse net- 
work. The trabecule consist of rather dense fibrous tissue 
with scattered nuclei. Far back from the edge this 
becomes reduced to little more than a layer of small 
nuclei and a few fine fibres. Delicate bridges of fibrous 
tissue unite the two epidermes, so that the whole cavity 
in the interior of the mantle lobe is divided into a system 
of inter-communicating spaces which are generally empty 
in sections, but are most probably blood sinuses. The 
inner epidermis 1s composed of flat squamous cells. Near 
the point of attachment of the mantle lobe to the body- 
wall the former becomes much thicker, and the spongy 
tissue in its interior attains a greater development. 
If now, the mantle lobe being removed, the labial palps 
be cut away along their attached borders, and the gills be 
carefully removed by cutting close to their bases, the 
portion of the body lying between the adductors. is laid 
bare. The base of the ctenidium (B7’., fig. 3) extends 
downwards obliquely from the region of the body extend- 
ing up into the umbones, to the lower horizontal level of 
the posterior adductor. Here the bases of the right and 
left ctenidia become free from the body-wall, and continue 
to pass ventrally and posteriorly till their posterior extrem- 
ities fuse with each other in the middle line, and with the 
horizontal shelf, referred to above, as formed by the 
extension inwards of the first fusion of the mantle lobes 
