56 ON THE ANATOMY OF MEGASCOLIDES AUSTRALIS, 
which are smaller, and thrown into folds externally. Amongst the fibres are 
numerous blood-vessels. The layer of longitudinal fibres consists of groups of fibres, 
each of which is angular in section. The groups are surrounded by connective 
tissue, a layer of which lies between them and the ccelomic epithelium. The 
nephridium consists of a number of intracellular ducts cut in section, and surrounded 
by a mass of connective tissue cells, whose outlines cannot be distinguished. 
Amongst them ramify very many blood-vessels (b.v.) A special blood-vessel 
accompanies the duet through the body wall. The duct is thrown into folds in the 
latter, and hence presents the appearance of a series of sections. The intracellular 
opens into the intercellular, just within the circular layer of muscle fibres, and the 
intercellular part runs straight to the exterior opening through the special spherical 
structure formed by the epidermic cells. 
Fig. 19.—A_ transverse section through the ventral nerve cord in the posterior 
region of the body. The section is taken through the part lying between the origins 
of the lateral nerve branches. The whole is surrounded by connective tissue, which 
on either side passes off to the supporting laminz running to the body wall, 
Special muscle fibres (m.) running along each side of the cord are cut through. The 
nervous matter is distinguishable into two parts, (1) an inner double cord of nerve 
fibres, and (2) a darker looking outer layer of fibres and ganglion cells, confined to the 
lateral and ventral aspects. The ganglion cells are large, and as a rule have but one 
process, which runs into the central part. Dorsally are four giant fibres, each with a 
special sheath of wavy-looking connective tissue fibres, The ccelomic epithelial cells 
are more columnar on the ventral than the dorsal surface. 
Fig. 20.—A portion of the alimentary canal within the last twenty segments of 
the body, together with the body wall ventrally. The strong septa at right angles to 
the canal are seen with their supports radially arranged. The dorsal blood-vessel 
(d. bv.) is surrounded by a white tubular structure (w), from which in each segment 
diverticula, irregularly arranged, are given off. The smaller nephridia are seen to lie 
in the posterior part of each segment. 
PLATE 5. 
bv ... blood-vessel. 
ct ... connective tissue. 
dp ... dorsal pore. 
ep ... epithelium of alimentary canal (Fig. 24.) of receptaculum 
seminis (Hig. 25). 
1 ... straight portion of larger nephridium. 
musc cive ... circular layer of muscle fibres. 
musc long ... longitudinal layer of muscle fibres. 
