210 ZOOLOGY 
the shell, it terminates in a trifid lobe. Dorsal to it is 
the oral cone or head, at the end of which the mouth opens, 
surrounded by short pinnate tentacles (Fig. 123). A buccal 
mass and a radula are present; two liver lobes symmetrically 
placed open into the stomach, from which the intestine passes 
to open by the anus in the ventral middle line. 
A right and left nephridium are present, and open to the 
exterior on either side of the anus. There is no heart, but 
the coelom contains a colourless blood. At the base of the 
oral cone a number of ctenidial filaments have their origin. 
These are capable of very considerable extension. The nervous 
system consists of a pair of cerebral ganglia, close to which he 
the pleural ganglia. Long commissures connect the cerebral 
with the pedal ganglia, The visceral commissure is also long, 
and bears the olfactory ganglia, situated in front of the anus, in 
the same position as in Lamellibranchs. The generative gland is 
alike in both sexes; it is situated dorsally, and its products 
make their exit through the right nephridium. 
CLASS Cephalopoda. 
CHARACTERISTICS.—Bilaterally symmetrical Glossophora. The 
visceral hump is elongated, not twisted ; the sub-pallial chamber 
is chiefly developed posteriorly, and contains the gills, anus, 
and excretory pores. The shell may be external or internal, 
in a few cases it 1s absent. The foot has grown round the 
head, and is broken wp into the characteristic arms of the 
Cephalopoda, provided with suckers. Part of the foot forms 
a funnel-like siphon, which guides the water as it is expelled 
from the pallial cavity. The vascular system is well 
developed, in addition to the central heart consisting of a 
ventricle and two auricles, an accessory branchial heart exists 
at the base of each gill in all but Nautilus. Powerful beak- 
like horny or calcareous jaws guard the mouth, and the 
radula is well developed. Chromatophores are present in the 
integument. The Cephalopoda are dioecious. 
The Cephalopoda are divided into two orders: (i.) The 
TETRABRANCHIATA or the TENTACULIFERA and (1i.) the DI- 
BRANCHIATA or the ACETABULIFERA. 
