68 THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
passed down the neck may be gathered from the fact that no large granules occur in 
the deeper part of the cell. Figure 18 represents a group of these cells drawn from 
the specimen referred to. , 
Figure 17 shows another modification of the digestive cells, found in a 
diverticulum a short distance behind the pharynx of another specimen. ‘The animal 
in this case was simply preserved in alcohol, and the sections cut by the paraffin 
method. The cells in question are globular, and considerably smaller than the 
ordinary digestive cells described at first. ach contains a nucleus, a very small 
quantity of protoplasm, greatly vacuolated, and a number of large, highly refractive 
granules. I have not found them arranged in a definite layer, but scattered about in 
the lumen of the diverticulum amongst quantities of large and small granules. 
They are very possibly cells which have completed their digestive functions and 
are undergoing dissolution. 
I can fully confirm von Kennel’s observations with regard to the heaps of granules 
of which, in most sections, the wall of the alimentary canal appears to be composed ; 
they are doubtless derived from the breaking down of cells filled with granules, such 
as those which I have been describing. The breaking down of these cells is 
probably partly, but not entirely, due to the action of the re-agents, for I believe 
the granules to be mostly excretory products which are sooner or later naturally set 
free by the breaking down of the cells, and then discharged through the mouth. 
In short, the following appears to me to be the most correct view concerning the 
nature of the lining epithelium of the alimentary canal. It consists primitively of a 
single layer of amceboid cells, which take in and digest food particles. At the anterior 
end of the alimentary canal, where we may suppose that only a little food can find its 
way, these cells retain their amceboid character, and remain in a single layer. 
Nearer the mouth, however, where there is more food to be digested, the cells become 
so numerous that there is no longer room for them in a single layer, and we 
consequently find them in irregular heaps. Even these cells are probably amceboid, 
at any vate in the earlier stages of their existence; they soon, however, become 
densely charged with granules (excretory products), and their protoplasm at the same 
time seems to dwindle away, so that ultimately we have mere thin-walled bags full of 
granules, which, sometimes at any rate, become rounded off and no longer form a 
definite layer. Finally the cell wall ruptures, and the granules are discharged into 
the lumen of the alimentary canal, thence to be ejected through the mouth. 
A somewhat similar condition of affairs has been described by Hallez (5), in the 
case of Mesostomum ehrenbergu. In this species the walls of the intestine are formed 
of tabular cells. During digestion these cells swell considerably, until they attain 
ten times their original volume; their contents become more transparent, and 
