THE REGENERATION OF THE PHARYNX IN 
PLANARIA MACULATA. 
HENRIETTA F. THACHER. 
In a paper on Planaria maculata, published in 1898, Morgan 
called attention to an important feature of the regeneration of 
the pharynx, namely, that in regenerating pieces which were 
cut anterior to the old pharynx, the new pharynx forms “at 
the edge of the old tissue, but lying for the most part within 
the zew material," while if the cut were made posterior to the 
pharynx the new organ forms in the anterior end of the o/d 
tissue. During the next two years there appeared a number of 
papers describing experiments on the power of regeneration in 
planarians, but giving no further knowledge of the develop- 
ment of the pharynx except that to be derived from general 
statements of the various positions it may assume in the regen- 
erating pieces. More recently a paper by Bardeen on the 
physiology of Planaria maculata has taken up the formation 
of the pharynx in this species and given a somewhat detailed 
account of it. 
In studying the origin and growth of the new pharynx, I 
wished to find out if there were any marked difference between 
its formation in the zew tissue of the anterior piece and in the 
old tissue of the posterior piece, since the conditions for regen- 
eration seemed so unlike in the two cases. At the same time 
I was interested in observing in the posterior pieces what might 
be the influence of the reproductive organs when present in the 
region where we should expect the pharynx to appear, and if, 
under these conditions, the already existing cavities and external 
opening can be made use of. In this connection I examined 
s^ries of regenerating posterior pieces in which the cut had been 
made (1) just posterior to the pharynx, but at a time of year when 
the reproductive organs have disappeared ; (2) anterior to these 
organs when they are fully developed ; and (3) posterior to them. 
