THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 75 
lateral surfaces of the animal the rods are frequently so numerous as entirely to 
conceal the true structure of the epidermis, and make it appear as though the latter 
were composed solely of closely packed rods. 
Beneath the epidermis the rods are concentrated in a special zone lying just 
below the nerve sheath, and hence also below the external longitudinal layer of muscles, 
as described by Moseley. ‘This zone is a very conspicuous feature in all vertical 
sections of the animal, as shown in figures 4,10, and 15. It is best developed on the 
dorsal surface and well on the lateral surfaces, but on the ventral surface the rods 
become much fewer in number and smaller in size. In this special zone the rods are 
arranged in faggot-like groups or bundles. Hach bundle is usually spindle-shaped, 
but the inner ends of the rods composing it are more closely packed than the outer 
ends, which tend to separate. Figure 23 represents such a bundle, in which the 
outer ends of the rods are more separated than usual. The form, structure, and 
mode of staming of the individual rods in this position agree so exactly with what 
has been just described for the ejected rods on the surface of the animal as to leave 
no doubt as to the identity of the two. In figure 23 the ends of the rods are 
blunter than is usually the case; possibly the extreme tips have been cut off in 
the section. In the fully-developed groups of rods, occurrimg in the special zone 
of rod-like bodies, it is no longer possible to discover traces of the original mother- 
cell in which they were developed; it seems to have entirely disappeared, though 
its previous existence is still indicated by the grouping of the rods. Between the 
special zone and the epidermis, rod-like bodies, still assembled in groups, are 
frequently met with at different levels on their way to the surface, as I have 
represented in figure 15, but there are no traces of any special ducts through which 
they pass. In figure 19, again, groups of rod-like bodies, in transverse section, are 
seen on their way to the surface, between the longitudinal muscle bands. 
The young mother cells of the rod-like bodies, still recognisable as distinct cells, 
occur scattered about just beneath the special zone. They are not so numerous as 
one would be naturally led to expect from the great numbers of rods occurring in the 
special zone and epidermis. They are very small, and when first recognisable already 
elongated so as to be spindled-shaped (Figs. 20, 21). Each contains a large, granular 
nucleus, and the protoplasmic body of the cell is very small and difficult to make out. 
Around the nucleus the rods appear as shown in the figures; first of all as a few 
slender, darkly staining streaks. They soon, however, increase so greatly in size and 
numbers as to obscure everything else, though still tightly enclosed in the delicate, 
extended mother cell (Fig. 22). In the special zone, as already stated, no trace of the 
mother cell remains visible, and the rods frequently tend to become separated at their 
outer ends, indicating that the wall of the mother cell has been ruptured in this 
position. 
