556 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY, 
the embryonic pharynx. As he especially states that all trace of 
the embryonic pharynx disappears before the adult pharynx begins, 
I think it not unlikely that he may have been mistaken in supposing 
that the place of the new pharynx was identical with that of the 
embryonic one, and that the embryonic pharynx of Dendrocoelum 
lacteiim may lie at the point indicated by the mass of cells in Ijima’s 
figure, which is identical with the point at which it is found still 
persisting in _P. maculata. 
The exact position would be hard to establish in Dendrocoelum 
lacteum since the first pharynx disappears before the second can be 
distinguished, but in P. macidata where both occur together, their 
relative positions can be at once determined, and since it would be 
rather strange to have such an entirely different relation in forms 
so nearly alike in all their general structure as the planarians, I 
believe the mass of cells indicated at this position in Ijima’s figure 
may also mark the location of the embryonic pharynx in De7idro- 
coelum lacteum. 
Summary. 
Specimens of this planarian collected from several localities and 
resembling each other so closely that one can hardly believe they 
are even different varieties of Planaria macidata.^ show consider¬ 
able differences in their life histories. In some localities the spe¬ 
cies seems to have reproduced exclusively, so far as the observations 
go, by fission, in others only by the sexual process, while there are 
still others where both processes occur at different seasons. A pos¬ 
sible explanation of this is that the reproduction by fission may 
replace the sexual reproduction for a terra of years though the time 
(three years) over which my observations extended is not sufficient 
to establish this fully. 
The characteristic feature of the normal fission occurring in this 
form is that it takes place without the previous appearance of any 
furrow at the place of division and without any previous develop¬ 
ment of the new organs necessary for two complete planarians. 
Hence there is produced the same appearance as in a specimen arti¬ 
ficially cut in two at a definite point behind the pharynx. 
From a study of the histological details in the regeneration after 
