638 THE AMERICAN NATURALIST. | [Vor. XXXVI. 
does not continue after the structure is well organized, and the 
latter part of the time needed for the regeneration of this 
organ is occupied in changing the parenchyma cells into the 
different tissues. Up to the time when the muscles appear, 
the cells still remain crowded together and show by their deep 
color the presence of unusually dense protoplasm. After the 
muscles are well formed the tissue assumes a less dense appear- 
ance, and this change arises apparently at the same time in 
the cells throughout the new tissue. Deeply staining masses, 
as of mucous, can also be seen, so that the tissue soon resem- 
bles that of the normal worm. 
The process of formation of a new pharynx in the old tissue 
of the posterior piece seems to be very similar, and equally 
simple during the nine months of the year when the repro- 
ductive organs are absent. The overgrowth of the cut sur- 
face and the increase in the number of dividing cells is just 
as was found in the anterior piece. The pharynx thickening, 
however, appears about twelve hours later than in the former 
case, z.e., about the end of the third day, and is usually notice- 
able shortly after the two branches of the digestive tract have 
joined. But that the pharynx is formed with relation to the 
“axial gut," as Bardeen states, I am not prepared to say, as 
occasionally a case is found in which the branches have not 
met, although a thickening is present, and often in a slide 
showing a conspicuous gathering of cells the union between 
the intestines has barely taken place. The pharynx forms 4 
short distance posterior to the cut, in the old tissue. It is 
first made visible by the shifting of the axes of some of the 
cells, which now direct themselves toward the new point of 
activity, and the thickening increases rapidly (Fig. 3). The 
cavities open up just as in the anterior piece, but the chamber 
is apt to be much longer and more irregular in outline than 
in the other case. Later the enlarged cavity rounds off 
so that the chamber resumes its normal size. The central 
cavity of the digestive tract enlarges in a posterior direction, 
and at the same time the pharynx thickening is added to by 
cells at the anterior end; thus, by the time the pharynx !5 
ready to open up, the original space between it and the 
