PARASITOLOGY

out with the faeces; and (2) anapolytic — the proglottids are detained and the eggs are

released through a uterine pore.

3.8.3.4 The tegument

The tegument is the external covering of cestodes and trematodes and is made up of a

syncitial protoplasmic layer divided into two zones: the distal cytoplasm and the peri-

nuclear cytoplasm. The inner perinuclear cytoplasm is a nucleated layer containing tegu-

mental cells and the distal cytoplasm is a syncitial layer which consists of a cytoplasmic

extension of the perinuclear cytoplasm. Within the cytoplasmic layers are the organelles

(mitochondria, Golgi bodies, endoplasmic reticulum), contractile vacuoles, dense

secretory bodies and pinosomes.

The external surface of the distal cytoplasm has numerous micro-extensions known

as the microthrix. This layer increases the surface area for absorption as well as possibly

helping adhesion to gut wall.

A layer of mucopolysaccharides and glycoproteins forms a ‘layer’ — the glycocalyx

— covering the microthrix. The glycocalyx can bind most enzymes and this may be the

site of membrane or contact digestion and then the products of digestion are absorbed

through the tegument (see Fig. 3.3).

3.8.3.5 The parenchyma

This is a network of mesenchymal cells that makes up the ‘middle layer’. All the inter-

nal organs lie within this complex network of cells and the spaces within the network

are filled with fluid containing glycogen, a food reserve.

PARASITOLOGY

Glycocalyx

Michrotriches

Layer of dense granular

bodies

Distal cytoplasm

Golgi complex

Endoplasmic reticulum

Cytoplasmic tubules

Nucleus

Muscle blocks

Mitochondrion

Nucleus

Perinuclear cytoplasm

• Figure 3.3The outer
  layer of a cestode is
  a living layer known
  as a tegument. At the
  host–parasite interface
  is the glycocalyx.
  Microtriches extend
  the surface area. The
  tegument is a syncitium
  ie a non-cellular,
  multinucleate layer with
  the nuclei and organelles
  embedded in the inner
  layers of the tegument.
  The tegument is a
  metabolically active layer
  and all nutrients are
  absorbed through the
  tegument.