Cyclophyllidea. At the very tip of the scolex of the Cyclophyllidea there may be a
retractable ring of hooks, the rostellum. Behind the scolex is the neck region which is a
regenerative region. This is where new proglottids are continuously formed to replace
those lost at the posterior end. The chain of proglottids formed is known as a strobila.
3.8.3.3 The proglottid
The youngest proglottids are immediately behind the neck region. As they develop they
appear to be separated from the one another by external constrictions.
Each proglottid (see Fig. 3.2) has an external living tegument, male and female
reproductive organs, a lateral longitudinal nerve cord and a median longitudinal nerve
cord (both are connected to a central nerve ring in the scolex). Scattered within the proglot-
tid are flame cells linked to dorsal and ventral (‘collecting’) vessels which link up with
vessels from neighbouring proglottids.
Mature proglottids become filled with eggs (gravid). There are two types of proglot-
tid (sometimes called segments): (1) apolytic — the gravid proglottids are shed and pass
PLATYHELMINTHSIndividual hookRostellumSuckers‘Neck’Region for generation of
new proglottidsExcretory canal
Vas deferens
Cirrus pouch
Genital pore
Vagina
Ovary
TestesUterusVitelline duct
Vitelline gland- Figure 3.1An adult
tapeworm (cestode)
normally inhabits the gut
of a vertebrate. The scolex
at the anterior (‘head’) end
is equipped with an
attachment ‘organ’. The
Cyclophyllidean cestodes
have four suckers just
below an apical rostellum.
The rostellum has one or
more rows of hooks. The
shape and size of the
hooks varies according
to the individual species.
Behind the scolex is the
‘neck’ region that
generates the new
proglottids. - Figure 3.2The main
body of a tapeworm is
made up of a series of
repeating segments and a
single segment is known
as a proglottid. Each
proglottid (except for the
Dioecocestodidae) contains
a complete set of both
male and female
reproductive organs
embedded in a layer of
parenchyma tissue.