3.8.3.6 The muscle structure
Beneath the tegument are two layers of myoblasts, muscle cells with lateral fibre-like out-
growths (fibrillae). One layer forms transverse or cuticular muscles with the fibrillae
running transversely, the other layer forms longitudinal muscles (with longitudinal
fibrillae). The muscle cells are made up of a non-contractile portion containing the
nucleus and a myofibrillar portion that contains the myofilaments.
3.8.3.7 The nervous system
The major nerve ganglia are concentrated in the scolex. There are three nerve rings. The
innermost, the central nerve ring, is the largest and links two lateral ganglia with a cent-
ral ganglion. From the central nerve ganglion four median longitudinal nerve cords run
posteriorly through the proglottids; and from the two lateral ganglia four lateral longi-
tudinal nerve cords run backwards through the proglottids.
From each of the lateral ganglia arises an anterior longitudinal nerve. These join into
the two rostellar ganglia which are linked by the rostellar nerve ring. The rostellar nerve
ring supplies the rostellum with nerve cells and connects into the apical nerve ring (just
beneath the rostellum).
The lateral ganglia also supply the suckers or adhesive organs with nerves and within
the tegument there are numerous ciliated sensory receptors.
3.8.3.8 The excretory system
The basic functioning unit of the excretory system is a flame cell. These are cells in
which one of the end cytoplasmic ‘walls’ is extruded into a flask-shaped long tubule that
feeds into a collecting duct. The actual cell has a large nucleus with mitochondria in the
cytoplasm. Cilia extend out of the cytoplasm into the lumen of the tubule; and the upper
walls of the tubule carry a series of small projections, the leprotriches.
The beating of the cilia causes fluids that have seeped into the flask-shaped end of the
cell into the tubular extension. The fluids then move away from the cell into the collecting
ducts. This process removes excess liquid waste from the body, while a certain amount
of reabsorption occurs along the walls of the collecting tubule. The liquid waste collects
in a ‘bladder’ and then empties via an excretory pore.
3.8.3.9 The reproductive organs
Each proglottid contains a complete set of male and female reproductive organs. The only
exception among the cestodes is found in the genus Dioecocestuswhere the male and
female organs are found in separate individuals. The basic cestode arrangement of the organs
in each proglottid is as follows:
MaleThe testes are paired and tend to be at either side of one end of the proglottid.
From each testis emerges a collecting duct the vas efferensand these merge to form a
single duct the vas deferens. The vas deferensleads into a short muscular tube, the cirrus,
situated at one side of the proglottid in a pouch, the cirrus pouch, and this structure has
an external opening, the genital pore.
FemaleThere is either a single large ovary or a pair of ovaries linked into a com-
mon bulbous collecting tubule (see Fig. 3.4). There are several ducts exiting from the
common tubule. Firstly there is the oviduct which ends in a coiled blind-ending uterus.
On the opposite side is the duct which runs into the vagina situated in the cirrus pouch
and opens to the exterior at the genital pore. At the bottom end of the common tubule
is the vitelline duct that drains the vitelline glands. These supply material for egg
membranes.
PLATYHELMINTHS