No. 428.] PHARYNX IN PLANARIA MACULATA. 639 
digestive tract is bridged over (Figs. 4, 5). The appearance and 
development of the lumen, muscle bands, and normal spongy 
tissue is identical with that in the anterior pieces, and the 
posterior piece is also ready to feed in seven days. 
Summing up these results, it appears that the regeneration 
of the pharynx in the new and in the old tissue is much the 
same, (1) as to the origin and migration of the cells, (2) as to 
the formation of the two cavities (the chamber and the lumen 
of the pharynx), and (3) as to the differentiation of the cells 
into the normal tissues. They differ (1) in the length of time 
that elapses before the pharynx thickening shows itself (about 
twelve hours more being required for its appearance in the old 
tissue than in the new), (2) in the position of the developing 

— ko 
Fic. 4. Fic. 5. 
Fics. 4, 5. — Stages in development of pharynx in posterior piece. 
pharynx with regard to the central digestive cavity, and (3) 
in the size of the pharyngeal chamber as shown by its early 
irregularities in the posterior piece. The last two differences 
are probably due to the disposition of the digestive branches 
in the two cases. 
In the early part of the summer the reproductive organs of 
this species are fully developed, and regeneration under these 
conditions is especially interesting. The genital apparatus lies 
for the most part in the region just between the pharyngeal 
and genital pores, so that when an animal is cut just posterior 
to the pharynx these organs occupy the region where the 
new pharynx should develop. Under these conditions there 
is no sign of the growth for the new pharynx until towards 
the end of the fourth day, when a small collection of cells can 
