THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 69 
sometimes fatty drops appear in the interior. At the same time the nucleus 
disappears, after having become reticulate. Soon the cell, considerably distended, 
appears as a perfectly transparent sphere, without proper walls, apparently formed of 
a very thick liquid, and enclosing in its centre a refractive globule, resembling a 
concretion. At this stage the sphere detaches itself from the wall of the intestine, 
and forms a veritable deliquium. The refractive globules, or concretions, are finally 
discharged through the mouth. 
Hallez also observes, ‘‘ ces sphéres transparentes, avec leur concrétion centrale, 
qui remplissent |’ intestin de tous les Turbellariés (Rhabdoceles et Dendroceles), et 
qui parfois se fusionnent plusieurs ensemble, ont certainement été vues par tous les 
naturalistes qui ont observés de ces animaux, mais jusqu’a présent personne, & ma 
connaissance, n’avait déterminé ni leur origine ni leur nature, ni leur réle. 
‘“‘ Le role de cette sécrétion doit consister trés-vraisemblablement 4 modefier la 
nature chimique des aliments, de maniére a permettre la diffusion de ceux-ci a 
travers la paroi intestinale.”’ 
It appears to me, however, that these refractive particles are not to be regarded 
as a secretion at all, but as excretory products ; considering that digestion is almost 
certainly intra-cellular, we should scarcely expect to find a special digestive secretion, 
while the fact, observed by Hallez himself, that the particles are ultimately 
discharged through the mouth, argues strongly in favour of their excretionary nature. 
Judging from Hallez’ figure (Plate VI., Fig. 21), the tabular cells which form 
the walls of the alimentary canal appear to be ameboid. A layer of similar flattened 
cells occurs in the anterior portion of the small chamber (Fig. 10.) which terminates 
the alimentary canal in front in Geoplana spencert. 
I have not observed any of the unicellular glands described by von Kennel as 
occurring between the ordinary digestive cells, and it seems to me possible that the 
supposed glands are merely stages in the life-history.of the latter. My own observations 
also do not tend to confirm his statement that the nuclei in the adult animals are so 
numerous, and the cells so small, that it is difficult to distinguish them. It 
is certainly a very difficult matter to make out the cell boundaries, owing to the great 
number of granules which usually occur, but the nuclei, where visible, always 
appeared to me to be rather small in comparison with the size of the whole cell, as 
von Kennel himself figures in the young Planaria lugubris. 
Like von Kennel, I have nowhere observed cilia on the digestive epithelium of 
the alimentary canal, nor does it seem in any way probable that they exist in this 
