MUSEUM OF COMPARATIVE ZOÖLOGY. 19 
anal end than in the last stage, and there is a second cavity below the 
atrium, from which it is separated by a line of nuclei. This is plainly 
an early stage in the formation of the alimentary tract, which thus first 
appears at the anal side of the bud, as in Phylactolemata, and is progres- 
sively formed towards the oral end. An appearance similar to the one 
figured would be given by a slightly oblique section of a later stage; but 
this section is strictly sagittal, and no trace of the lumen appears in adja- 
cent sections, I have found a similar condition in a series of longitu- 
dinal sections at right angles to the sagittal plane of the bud (Plate IV. 
Figs. 39 and 40). Figure 39 shows that the atrio-pharyngeal cavity is 
first developed at the anal end, and in Figure 40, which is three sections 
(about 15 u) below Figure 39, the anal end only of the alimentary tract 
is formed. It is worthy of notice that the cells of the mesodermic layer 
of the bud are often greatly vacuolated at this stage, as in Figures 39 and 
40, vac. Braem (90, p. 126) says of this stage: “ Die der Resorption 
dienenden Darmabschnitte, Magen und Enddarm, werden gemeinsam an- 
gelegt, indem auf jeder Seite der Knospe eine Längsfalte die Wandungen 
nach innen und gegen einander zu einbiegt, worauf die benachbarten 
Theile des inneren Blattes verschmelzen und so durch eine Art Abschnür- 
ung das primäre Knospenlumen in den vorderen Atrialraum und die 
hintere Darmhöhle getrennt wird.” While I thoroughly agree with this 
statement, the additional fact of the formation of the tract progressing 
from the anal towards the oral end is interesting, in that it shows that the 
process of formation of the organ in Paludicella is fundamentally similar 
to, although differing slightly in detail from, that of the Phylactolamata. 
Figure 24 shows in sagittal section a still later stage in the development 
of the alimentary tract. A cross section of this stage is seen in Figure 
30 (Plate IV.), in which the separation of atrial and gastric cavities is 
demonstrated. The inner layer of the bud is here seen to be separated 
from the ectoderm by a distinct line, and, to a certain extent, even by 
the mesoderm. The distal (oral) part of the cavity of the alimentary 
tract next becomes considerably enlarged to form the stomach (Fig. 25). 
The outer layer of the bud, ms’drm., penetrates between the stomach 
and the atrium, and a depression is formed at the bottom of the atrial 
chamber which will give rise to the @sophagus, Even at this stage the 
@sophagus is not in communication with the stomach, but their cavities 
are separated by two layers of cells of the inner layer of the bud. These 
two layers become those of the cardiac valve (Plate IV. Fig. 36, vlw. cr.). 
By a further comparison of Figures 25 and 36 it will be noticed that, 
whereas in the earlier stage, as in Endoprocta, there is no cocum to the 
