20 THE ESSEX NATURALIST
have a typical molluscan anatomy, yet so highly organised have
they become that in some respects they are comparable with the
vertebrates. 
There is still a mantle and mantle cavity, but unlike the other
classes the Cephalopods have developed the former into a
powerful muscular structure which drives water out through a
funnel, giving to these animals a form of powerful jet propul-
sion. The funnel is the remodelled molluscan foot. From the
head spring eight (Octopus) or ten (squids) tentacles, power-
ful grasping organs bearing one or two rows of suckers. The
extra pair of arms in squids can be retracted into pockets in
which they are normally carried, and from which they are shot
out to grasp the prey.
The eyes of Cephalopods are similar to those of vertebrates
and their brains are so highly organised that they have been
used by Young and Boycott (1950) for the study of various
aspects of behaviour and learning.
Within the mantle cavity are the usual molluscan gills but
these have additional pumping devices ("branchial hearts") to
speed the passage of the blood and so to provide a more rapid
supply of oxygen for the tissues of these active animals, some
of which rival the pelagic fishes in the speed and precision of
their movements.
The Cephalopods include the largest members of the Mol-
lusca, some deep-sea forms being recorded as having reached
60 feet in length from the apex of the body to the tips of the
tentacles. All are marine and around our coasts the following
are fairly common :.—the common Octopus (Octopus vulgaris),
the lesser Octopus (Eledone cirrhosa), the cuttlefishes
(Eusepia officinalis and Parasepia elegans, Pl. 3), the
Squid (Loligo forbesi) and the small burrowing forms Rossia
and Heterosepiola (Pl. 3).
Details of the remaining two small classes of Molluscs, viz.
the Solenogastres (worm-like forms ectoparasitic upon hydroid
colonies) and the Scaphopoda or Elephant's tusk shells (bur-
rowing filter feeders) are omitted, but I hope that in what has
been said I have been able to convey to you some idea of the
range and variety of animals in this important Phylum, and
some of my own interest and pleasure in the study of them.