THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 65 
appearance, and their evident connection with irregular masses of mucous lying 
beneath the epidermis, at once reveal their true nature. Although the true columnar 
cells are thus completely hidden by the masses of mucous, their cilia are still plainly 
visible on the surface, as will be seen by reference to figure 29. 
Immediately beneath the epidermis there appears a thin layer of longitudinal 
muscle fibres, and beneath this again a thin layer of circular muscles, exactly as 
described by von Kennel (3) in the forms examined by him. Thus it appears that 
the relative position of the longitudinal and circular layers of muscles is here 
exactly the reverse of what it is in the integument generally. The thin layer of 
circular muscles is followed, after an interval in which glandular tissue and nuclei, 
with only a few fibres, occur, by a very thick layer of longitudinal muscles, which 
demand special attention on account of certain peculiarities in their component fibres. 
These are much thicker and stain much more deeply than the ordinary muscle 
fibres, and they are also granular. They are very conspicuous in longitudinal 
sections of the pharynx, and in general appearance resemble glandular tissue, but 
instead of running towards the surface of the pharynx, as would be the case were 
they glandular structures, they run parallel with it. Beneath this layer of longitudinal 
fibres comes a thick layer of circular fibres, exhibiting the ordinary histological 
characters and immediately surrounding the lumen of the pharynx. 
In addition to the muscle layers thus enumerated there occur a number of 
radial fibres, running from the inner circular layer towards the outside, so that the 
agreement of the muscles of the pharynx in their arrangement with those described 
by von Kennel in the German land Planarians is complete. 
The lumen of the pharynx is lined by a single layer of rather large, irregular, 
columnar cells. These in section appear shrivelled and very much vacuolated ; they 
stain very lightly indeed, but each one has a very distinct oval nucleus which is 
coarsely granular and stains readily. The free surface of this epithelium is not 
smooth and even, but wavy and indented. I have not succeeded in detecting the line 
where it meets the ciliated epithelium of the outside of the pharynx, but the latter 
appears to be continued over the lip of the pharynx for some little distance. 
The three main Branches of the Alimentary Canal.—The lumen of the pharynx 
leads upwards and forwards into that of the great anterior branch of. the alimentary 
canal, and from the region where the two unite spring the two posterior lateral 
branches, running backwards, one on each side of the middle line. All three main 
branches are themselves very narrow and laterally compressed, but they give off on 
each side numerous blind diverticula, placed close together throughout the length of 
the alimentary canal. ‘hese diverticula are frequently branched, and, so far as I can 
