CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 541 
branches are everywhere growing out from the main rami at this 
time and it would not be strange if the process occurred elsewhere, 
but I have never seen anv such number of formative cells so inti- 
%/ 
mately connected with the gut as at the anterior tip of the new 
median ramus. As there is no other place where the gut is being 
remodeled to such a marked degree, this is what might be expected. 
That the formative cells of the parenchyma become added on to 
the gut in some places would seem a remarkable thing. The 
entire absence of observed cases of mitotic figures among gut nuclei 
during the time when the animal was growing so rapidly and the 
gut, of course, was likewise increasing, would be something at least 
in favor, if not evidence, of such a possibility. If it should be 
objected that neither had mitosis been seen in the ectoderm, I can 
call attention to the way in which the rhabdites obscure many 
ectodermal nuclei while the nuclei of the gut are readily seen. It 
is a difficult case to prove, but I can only believe from such instan¬ 
ces as are shown in figures 89 and 41 (plate 15) that where the 
new anterior ramus develops, some formative cells are added on and 
become gut cells. The intimate association of the two seems to 
admit of no other interpretation and if this is the case one must 
ascribe a remarkable versatilitv to the formative cells when their 
whole history in regeneration is considered. 
Whether the stages intermediate between parenchyma and for¬ 
mative cells represent parenchyma originating from formative cells- 
or the reverse, I leave an open question. That the formative cells 
which always occur in P. maculata in some numbers and in very 
great numbers during the season of fission are the basis for the 
regeneration folloAving normal fission, there can be no question. 
The existence of these cells and their r61e in regeneration in many 
other planarians and Rhabdocoeles have been recorded as shoAvn in 
my review of the subject. The latter have been thoroughly described 
in Rhabdocoeles, but not figured at all or thoroughly studied in 
the Triclads. My observations on the existence and r61e of such 
cells in P. maculata do not therefore stand alone. 
Starting with these formative cells which are continually increas¬ 
ing their number (see mitotic divisions in the figures), Ave get 
ectoderm, parenchyma, tissue of adult head, according to Flexener 
(’98) ganglion cells, pharynx, and probably parts of the gut. Aa 
far back as we can go, ciz.^ to the many self-sustaining and multi- 
