542 PKOCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
plying formative cells, everything is to be referred to these scarcely 
differentiated cells which may become almost anything. There is 
nothing in the ^^rocess, as I haye seen it, to indicate the degenera¬ 
tion of a highly specialized adult tissue into something simpler and 
from this the building of new organs. I regret exceedingly that I 
have not had the opportunity to study and compare what occurs in 
specimens artificially cut in two at just the place where fission nor¬ 
mally occurs. From Flexener’s description (’98) of P. maculata 
and from Keller’s statements (’94) as to the forms he studied, I can 
hardly see how there can be any different processes carried on in 
the regeneration after artificial cutting except that the excess of 
formative cells in animals which are multiplying asexually may 
make the process easier to follow. 
A structure which I have found to a varying extent in almost all 
the specimens examined from localities where fission is in progress, 
is shown at a? in a number of the figures (pL 13, fig. 35; pi. 14, 
fig. 37). There are lying in the parenchyma, mostly in the dorsal 
region, masses of large cells the outlines of which are not always 
easily discernible. They are not connected with the gut in any 
way nor do they resemble any structures which I have ever found 
described for the Planaria. They can best be characterized by say¬ 
ing that they have the appearance of gut cells without any vacuoles 
for their nuclei are very much like those of the gut and their 
cytoplasm stains in the same way, but they are not found connected 
with the gut in any way. They are, furthermore, not at all like 
the first beginnings of the reproductive organs and although I have 
held many theories as to their significance, I cannot offer even a 
plausible conjecture as to their meaning. My reason for mention¬ 
ing them is that they are usually a striking feature of animals from 
an asexual locality. 
The Axatomy of the Fully Developed Reproductive 
Organs. 
During the summer of 1898, while at the Marine biological labo¬ 
ratory, Woods Holl, Mass., I became interested in studying some 
very large specimens (15 to 20 mm. in length) of Planaria macu¬ 
lata. These were found in the ponds near Falmouth and with them 
large numbers of eggs which they lay during May and early June. 
i 
