BODY WALL OF FASCIOLA HEPATICA
The body wall of F. hepatica lacks a cellular layer of epidermis, unlike those of the turbellarians. However, it consists of a thick layer of cuticle followed by a thin basement membrane and underlying muscle layers surrounding the mesenchyma.
A tough resistant cuticle, made of a homogeneous layer of scleroprotein, covers the fluke and protects it from the juices of the host. It bears small spines, spinules or scales. The spinules anchor the fluke to the bile duct of the host, provide protection and facilitate locomotion.
The cuticle of F. indica has broad, stout, and blunt scales. The epidermis has been lost during development of the cercaria stage. However, the cuticle is secreted by special mesenchymal cells situated below muscle layers.
These cuticle secreting cells were believed to be sunken epidermal cells (Hein, 1904 and Roewer, 1906).
The lowest layer of the cuticle is a thin, delicate basement membrane. It demarcates the boundary between cuticle and muscle layers.
The basement membrane is followed by a sub-cuticular musculature. It consists of an outer layer of circular muscle fibres, middle layer of longitudinal muscle fibres and an inner layer of diagonal muscle fibres which are more developed in the anterior half of the body. All muscles are smooth. The muscles form stout bundles of radial fibres in the suckers.
Below the muscles is parenchyma (mesenchyme) having numerous loosely arranged uninucleate and bi-nucleate cells with syncytial network of fibres having fluid-filled spaces.
Some of these cells are large and provided with large processes extending up to the base of the cuticle to which they are said to secrete. In fact, the mesenchyme forms a packing material between the muscle layer and internal organs. It helps in the transport of nutrients and waste substances.
The body wall plays a significant role in the physiology of fluke. It provides protection, it is the site of gaseous exchange, various nitrogenous wastes are diffused out through it and it also helps in the absorption of amino acids to some extent.
Structure of Body Wall Under Electron Microscope
The electron microscopic studies of the body wall of F. hepatica by Threadgold (1963), Bils and Martin (1966) have clearly revealed that cuticle is a syncytial layer of protoplasm having mitochondria, endoplasmic canals, vacuoles and pinocytic vesicles.
Hence, cuticle is now referred to as the integument because it is metabolically active.
The tegument is continuous with tegument secreting cells lying in the mesenchyme. The outer integumental surface is thrown out into many fine projections which increase its area to facilitate the absorption of host’s fluid.
The tegument is also provided with many fine pore canals through which dissolved substances in the form of solution are absorbed into the mesenchyme.