
No. 428.] PHARYNX IN PLANARIA MACULATA. 637 
length, and the branches of the intestine have pushed back 
into it, while the central digestive cavity has also somewhat 
enlarged. Shortly after the lining of the lumen has formed, 
the muscle bands of the pharynx differentiate. They arise 
from cells just between the two epithelial layers ; they elongate 
and undergo some change in their constitution, since they 
stain with aniline orange very shortly after the lengthening 
process has begun. The change is first visible in the region 
where the pharynx is continuous with the body of the animal 

Fic. 2. Fic. 1. 
Fic. 1. — Large parenchyma cells migrating towards regenerating region. 
Fic. Que dies in anterior piece at close of fourth day. The lumen has just appeared. 
lumen ; Z, lateral digestive branch; C, pharynx chamber. 
Fic. = S ltd in n posterior piece at cione of third day. The lateral digestive branches have 
y ) There are many dividing cells present. 

and extends gradually posteriorly. So far as I could deter- 
mine, the circular muscles develop before the longitudinal, 
but if so, the difference in time is very slight. In the course 
of the fifth or sixth day the pharyngeal chamber opens to the 
exterior by an ectodermal invagination from the ventral sur- 
face, and shortly afterwards the animal begins to feed. 
The shape and size of the pharynx vary comparatively little 
after the inner lumen appears. At first, before the formation 
of this cavity, the shape is slightly pointed, but it soon becomes 
more regular and assumes the form of the normal pharynx, 
except for its length, which is only about once and a half or 
twice the breadth. The addition of cells at the anterior end 
