. In the entire animal the posterior end projects
slightly more than the anterior from the region of the umbones.

The animal possesses two nearly equal adductor muscles. The edges of the
mantle are united posteriorly except at the anal and branchial
apertures, which are placed at the ends of two very short siphons or
tubular prolongations of the mantle; the siphons bear a number of short
tentacles, and many of these are furnished with eye-spots. The foot is
very large and powerful; it can be protruded from the anterior aperture
between the mantle edges, and its outer part is bent sharply forwards
and terminates in a point. By means of this muscular foot the cockle
burrows rapidly in the muddy sand of the sea-shore, and it can also when
it is not buried perform considerable leaps by suddenly bending the
foot. The foot has a byssus gland on its posterior surface.

On either side of the body between the mantle and the foot are two flat
gills each composed of two lamellae. _Cardium_ belongs to the order of
Lamellibranchia in which the gills present the maximum of complexity,
the original vertical filaments of which they are composed being united
by interfilamentar and interlamellar junctions. In other respects the
anatomy of the cockle presents no important differences from that of a
typical Lamellibranch. The sexes are distinct, and the generative
opening is on the side of the body above the edge of the inner lamella
of the inner gill. The eggs are minute, and pass out into the sea-water
through the dorsal or exhalent siphon. The breeding season is April, May
and June. The larva for a time swims freely in the sea-water, having a
circlet of cilia round the body in front of the mouth, forming the
velum. The shell is developed on the dorsal surface behind the velum,
the foot on the opposite or ventral surface behind the mouth. After a
few days, when the mantle bearing the shell valves has developed so much
as to enclose the whole body, the young cockle sinks to the bottom and
commences to follow the habits of the adult. The usual size of the
cockle in its shell is from 1 to 2 in. in breadth.

The common cockle is regularly used as food by the poorer classes. It
occurs in abundance on sandy shores in all estuaries. At the mouth of
the Thames the gathering of cockles forms a considerable industry,
especially at Leigh. On the coast of Lancashire also the fishery, if it
may be so called, is of considerable importance. The cockl