CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 553 
a short distance. Such a stage might be represented by a diagram 
like figure 54 (plate 18). 
Following this, there are to be found along the line of each ovi¬ 
duct (pi. 18, fig. 55) many cords of cells seeming to have grown 
out from the original one ; at any rate they are connected with it. 
I can only conjecture how the oviduct is formed as I have not found 
any interpretable stages. The occurrence of the cord of cells such 
as is shown in figures 44 (plate 16) and 54 (plate 18), in just the 
position where the oviduct subsequently appears, suggests that this 
cell cord is in some way transformed into the oviduct. It has 
occurred to me that such a thing might come about by the migra¬ 
tion of the large cells (pi. 16, fig. 44) out from the main axis 
leaving the smaller nuclei embedded in their own fused cytoplasm, 
which subsequently becomes hollowed out to form the oviduct. 
The masses of larger cells would then remain connected with this 
as the finger-like processes of the young yolk glands (pi. 18, fig. 55) 
are later connected with the newly formed oviducts. In PlanaHa 
simpUssima^ I showed (;00a) that the yolk glands originated as out¬ 
growths from the oviducts, and this makes more plausible the origin 
of the oviduct in P. maculata in the manner I have just suggested. 
While I have not succeeded in ascertaining the histological proc¬ 
esses by which the oviducts are formed, they are laid down close 
to, if not exactly along, the main axes of the cell cords shown in 
figure 54 (plate 18) during the time that the young yolk glands 
(pi. 18, fig. 55, y) are appearing. An unquestionable oviduct is 
found in the stage which figure 55 represents, and posterior to the 
rudiments of the atrium this newly formed oviduct is continuous 
with a cord of cells such as in the earlier stage (pi. 18, fig. 54) 
extended from the ovary to the tail. The original cords of cells 
are no longer found in the area occupied by the oviducts. This 
suggests that the cord of cells shown in figure 54 has in some way 
been transformed into the oviduct over most of its length. In 
figure 55, the atrium is found far enough developed to have the 
different parts clearly marked. 
In the next figure (pi. 19, fig. 56), which is practically adult, there 
remains, stretching down into the tail upon either side, a branching ' 
rod of cells which is destined to become the yolk glands of the pos¬ 
terior end. It can be readily traced with its branches as indicated 
in the diagram and becomes continuous with the oviduct where the 
