creas, the anterior appendage can scarcely be seen. The enteron,
including one lung only, for the sake of simplicity, is shaded solid
black, while the liver and pancreas, with their ducts, are outlines with
unbroken lines. As in the preceding reconstruction no attempt is made to
show the gill clefts, and only the dorso-ventral profile of the enteron
is shown. Caudad to the pharynx, the enteron being more or less
cylindrical in section, this profile gives a good idea of its shape, but
in the pharyngeal region, where the lateral diameter is so much greater
than the dorso-ventral, the reconstruction gives but a poor idea of the
size of that part of the enteron.

The widely-open mouth, _m_, leads, with no line of demarkation, into the
pharynx, _ph_, which is of irregular outline and, as has been said, of
much greater lateral than dorso-ventral diameter.

The pharynx becomes gradually constricted to form the oesophagus, _oe_,
a very long and slender structure, which, as will be seen in cross
section, is, at this stage, solid for the greater part of its length. As
in the case of the pharynx, the lateral diameter of the oesophagus is
generally greater than the dorso-ventral diameter.

From the floor of the caudal part of the pharynx is pushed out the
trachea, _ta_. In the reconstruction, especially in the anterior end,
the trachea appears several times the diameter of the oesophagus; this
is due to the great thickness and indefiniteness of its walls rather
than to a greater diameter of its lumen.

At about the position of the line _ta_ the trachea divides into the two
bronchi (only one shown in the figure), which are somewhat enlarged at
the ends to form the lung rudiments, _lu_. While the trachea and bronchi
lie ventrad to the oesophagus, the lungs lie laterad and even dorsad to
the oesophagus and cardiac end of the stomach. Caudad to the heart and
in the region of the anterior appendages, _aa_, the oesophagus suddenly
enlarges to form the stomach, _i'_, which has now quite the outline of
the typical human stomach.

From the stomach the duodenum, _d_, extends, following a sort of
V-shaped course, towards the yolk-stalk, _ys_. In the region of the
yolk-stalk it is somewhat enlarged and ends in a blind sac like a
caecum. At the side of this sac is seen the opening of the enteron to
the yolk-stalk; the anterior and posterior intestinal portals are not
distinguishable from each other. From this point the hindgut, _hg_,
exten