
No. 428.] PHARYNX IN PLANARIA MACULATA. 635 
cells are found other cells which are specialized in function, — 
large rhabdite cells, lying just below the ectoderm and show- 
ing the rhabdites buried in the protoplasm, and the mucous 
cells, staining an intense blue; also, along the digestive tract, 
a few large granular cells for which Bardeen has suggested a 
digestive function. In addition, I have noticed some large 
cells staining with aniline orange, which seem to contain some 
such material as yolk. Whether this is a fourth kind or merely 
the digestive cells I have not been able to decide. There are 
also present elongated connective-tissue cells. 
Although the majority of the parenchyma cells show little 
protoplasm, scattered through the tissue of the normal unin- 
jured animal there are a good many cells whose nuclei resemble 
those of the ordinary parenchyma, but which have gathered 
about them an irregular mass of granular protoplasm. As 
many of these are in various stages of division, while I have 
found no division among the cells with less protoplasm, it is 
probable that the accretion of protoplasm is the usual fore- 
runner of division in the parenchyma cells, and that the number 
of the latter is constantly increasing even in normal planarians. 
While the number of these dividing cells differs individually, 
they are often very numerous and are confined to no one region 
of the body, except that they are more rare in the extreme 
tips. The dividing cells stand out very distinctly as they are 
larger and seldom have other cells near them. 
After the animals are cut, the amount of division increases 
somewhat throughout the whole body, but very markedly near 
the injured surface. Cells also migrate down into this region 
and form there a thickening which rapidly enlarges. That 
migration takes place is indicated by the long trails of proto- 
plasm that give to the cells a bipolar appearance with the axes 
directed towards the growing mass (Fig. 1), while in the normal 
planarian there is no such effect and the cells are more irreg- 
ular and rounded in outline. After the thickening has reached 
a certain degree of concentration there is rarely any cell divi- 
- Sion in the proliferated mass, but mitotic figures can frequently 
be found in the region near by, where the cell mass is less 
dense. Cells also continue to migrate into the new part and 
