636 THE AMERICAN NATURALIST. | [Vor. XXXVI. 
add to the new growth. The number of cells in the parenchym- 
atous tissue of the body itself is also usually much increased 
as the nuclei throughout continue dividing, and by the time 
the pharynx thickening appears, which is in the course of the 
third day, the tissue is filled with cells conspicuous on account 
of their greater amount of protoplasm. 
I shall consider first the growth of the pharynx in the ante- 
rior piece and then that in the posterior piece. By the time 
the proliferation of cells in the regenerating posterior tip 
is quite marked, a slight shift in the direction taken by 
some of the cells denotes the beginning of the new pharynx. 
The cells now collect just on the line between the. old and new 
tissue at the posterior end of the digestive tract, which has 
rounded off, and usually has begun to bud out side branches. 
As is true of the growing end, so here, when the thickening 
becomes marked, no division of cells can be found in it, but 
in the less dense tissue around it there are many dividing cells 
and apparently considerable cell migration towards the new 
growth. The collection of cells stains very deeply in compari- 
son with the old tissue near by, due probably to the greater 
amount of protoplasm in this region. 
The thickening for the pharynx grows until it is quite large, 
and then the split for the pharynx chamber begins. This 
opens up very rapidly as a narrow cavity running across the 
base of the thickening and up on the sides, being usually 
more advanced on the ventral than on the dorsal side. It !5 
at first irregular in outline, but the cells along the edge soon 
flatten out into a thin lining epithelium. As development 
proceeds, cells are added at the anterior end of the new 
pharynx, while there is no division in the compact mass of cells 
already collected (Fig. 2). About the fourth day the lumen 
of the pharynx itself appears in the center of the proliferation, 
due to an elongation and pulling apart of cells which become 
larger and thin walled and form the lining of the pharynx. 
This cavity gradually enlarges posteriorly to open into the 
pharynx chamber, and anteriorly to unite with the wall of 
the digestive tract, which then breaks through to join with ie 
The new region has in the mean time steadily increased !n 
