CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 555 
the gut lobes and so take possession of the dorsal region. So far as 
I can see, there is no particular area from which the yolk glands 
develop, as is the case, according to Woodworth’s description, in 
Phagocata gracilis. 
A Note on the Earlier Embryology of Planaria macidata. 
In following through the earlier embryology of P. maculata., I 
have not found that it offers any important difference from the 
descriptions of other species given by Ijima (’84) and Hallez (’79) 
save in one particular. This relates to the development of the 
pharynx and is explained in figure 51 (plate 17). This figure 
represents an embryo which has taken up all the available yolk cells 
through its embryonic pharynx and larval mouth {^ph' and Imo). 
This yolk (po) is seen within as a mass of disintegrating cells with 
nuclei. When the taking up of the yolk is just completed, the 
embryo is spherical with its embryonic pharynx at ‘one side, a stage 
which text book figures have made familiar to every one. The 
definite endodermal layer, which could at first be distinguished, can 
no longer be made out and the wall of the embryo seems to consist 
of a greatly flattened ectoderm (ec) and, closely applied to the inner 
side of this, scattered mesenchyme cells representing the endoderm 
and mesoderm. This spherical embryo of P. macidata flattens 
down as is shown in figure 51, and the inner cells increase in 
number along what is destined to become the ventral side of the 
adult. Posteriorly a mass {ph^) of these cells is especially notice¬ 
able and this becomes the adult pharynx by the process which has 
been often described. It will be seen that the lower flat side of the 
embryo of figure 51 represents the ventral surface of the adult and 
that the larval mouth (Imo) which leads through the larval pharynx 
into the gut cavity is on the future dorsal surface. This point 
has seemed to me worth noting, since from the descriptions of 
Ijima and Hallez the larval pharynx seems to open on that side of 
the embryo which becomes the ventral side of the adult and to have 
its longitudinal axis correspond to the vertical axis of the adult. 
Ijima’s figure 28 of plate 23 is a diagrammatic representation of 
almost the same stage as my figure 51, save that his figure shows 
a mass of ento-mesoderm cells over the area covered in my figure by 
