THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 61 
bands themselves, or perhaps sometimes wider, and it is through these spaces between 
the muscles that the rod-like bodies pass on their way out to the surface (Fig. 19). 
The muscular bands forming this layer are much stouter than those of the external 
- circular (or more properly oblique) layer. 
The external circular (or oblique) and external longitudinal layers of muscles 
are immediately contiguous, and it is a remarkable fact that the two together are not 
quite so thick as the epidermis of the dorsal surface (vide Figs. 4 and 15). 
Deep Muscular System.—The deep muscular system is separated, as in Bipalium 
and Rhynchodemus, from the superficial muscular system by a broad zone of tissue. 
Moseley (6) states that this intervening zone is occupied by loose radiating fibres and 
various skin organs. In Geoplana spenceri the radiating fibres (Fig. 15, 7.f.) are 
poorly developed. 
The deep muscular system itself (Fig. 15, y.) forms a layer around the alimentary 
canal considerably thicker than the last-named intervening zone, and very much 
thicker than the entire superficial system. It consists principally of two distinct sets 
of fibres, which are not arranged in definite layers but occur intermingled in the same 
mass. ‘The fibres of the one set are arranged longitudinally, as shown in the figure, 
while those of the second set run round the body, sometimes almost or quite 
circularly, so that their cut ends only (Fig. 15, c.f.) appear in longitudinal sections, 
but very often obliquely in two main directions, crossing one another at various 
angles. Between the various fibres of the deep muscular system we find glandular 
structures and a few nuclei. In the same layer are also found the radiating ends of 
the bolting muscles (Fig. 15, d.v.), whose main direction is dorso-ventral, but which 
run at various angles between the diverticula of the alimentary canal (vide Vig. 4). 
Moseley (6) mentions that specially stout muscular fibres, which he regards as 
derived from the circular portion of the deep layer, pass transversely immediately 
beneath the digestive tract. Very distinct fibres, which evidently correspond to 
these, are plainly visible in my transverse sections of Geoplana spenceri, running 
across above the longitudinal nerve cords, as shown in figure 4. This system of fibres, 
which is of very constant occurrence, may be conveniently termed ‘‘ supra-neural.” 
Thus the general musculature of the body agrees closely with that which 
Moseley has made known in other land Planarians. If, however, we try to draw any 
comparison with the muscular system of the fresh-water Tricladians, as described by 
Jijima (7), we find ourselves face to face with a somewhat difficult question. It is 
necessary first to remember that the only really distinct and well defined muscle 
layers—indeed, the only muscle layers at all—which can be considered as belonging to 
the superficial or ‘skin’? system in Geoplana, are the external circular (or oblique) 
and external longitudinal layers, which are evidently the homologues of the external 
circular and external longitudinal layers of Moseley. 
