CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 529 
In the head piece, after the normal fission, the remodeling goes 
on in such a way that the poition anterior to the phaiynx remains 
the same size, or at least the most careful measurements do not 
show any change in its proportions, while the portion posterior to 
the pharynx grows until it has completed the normal proportions. 
Figures 19, 28, 29, 30, and 32 o^ plates 10 and 11, will serve to 
illustrate this, as will also h*gure|' 11, plate 9, which represents the 
changes in outline at the posterior end of a head piece during the 
seven consecutive days following normal fission. Apparently the 
rapid growth of the animal when fed, masks to a certain extent the 
rearrangement of proportions, morpholaxis, which is so evident in 
pieces artificially cut from different parts of the worm for experi¬ 
ments in regeneration (Morgan, ’98, :00) and in the tail pieces (pi. 
9, fig. 2-7) which must go without food until the new pharynx 
develops. 
Internal Changes After Fission. 
Before describing the histological processes involved in the regen¬ 
eration after normal fission, it is necessary to describe the paren¬ 
chyma of this species, and I also take occasion to review to some 
extent the various descriptions which have been given by different 
authors of the normal parenchyma and its part in regeneration. 
Leaving out the gland cells, muscle and nerve fibers, and other 
organs which are set in the parenchyma as a matrix, the paren¬ 
chyma (pi. 16, fig. 43; pi. 15, fig. 41) in an adult P. maculata has 
the appearance of a syncytial mass, the cytoplasmic portion of 
which is relatively large. The structure of the cytoplasm is such 
that it has, after fixation, a varying number of vacuoles and irregu¬ 
lar clefts surrounded by a substance made up of what resemble 
the fibers of a network. The nuclei ( 712 ^) which seem properly to 
belong to this syncytium are set irregularly through it and as in a 
typical syncytium have no trace of a cell outline. Where the clefts 
and vacuoles are greatly increased in size and number, the tissue 
has something the appearance of scattered, multipolar cells, the proc¬ 
esses of which are everywhere continuous with those from neigh¬ 
boring cells. This condition is what is more frequently observed in 
the central parts of the adult planarian, but around the edges of the 
