ine was noted in connection with
figure 7. It is an irregular structure, consisting of a very thin outer
layer of mesoderm, lined with a single layer of flattened epithelial
cells.

Lying at a considerable distance ventrad to the main body of the
section, are seen the two sections of the small intestine, _i_,
surrounded by irregular strands of tissue from the umbilicus. The
structure of these two intestinal loops is about the same as in the more
anterior region described above.

Figure 7G, the last of this series, represents a section through the
cloaca, caudad to the urinary openings, in the plane 1060 of figure 7.
The epithelium of the cloaca is, of course, simply a continuation of
that of the surface of the body, somewhat thickened, perhaps, in the
deeper regions.

The intromittent organ, _io_, which projects cephalad from the wall of
the cloaca, is here seen as a three-pointed body of considerable size,
projecting ventrally from the body.

Figure 8 shows in outline the enteron, from the ventral aspect, of an
embryo of 20 cm. total length, or at about the time of hatching. The
drawing was made from a dissection and, for the sake of simplicity, only
the enteron, respiratory organs, heart, and thymus are shown. The jaw is
cut through on the left side and is turned over to the right, thus
bringing into view the roof of the mouth, _m_, and the dorsal side of
the tongue, _tn_. At the same time the pharynx, _ph_, and the wide
anterior end of the oesophagus, _oe_, are cut open, exposing the
glottis, _gs_, and vocal cords, _vc_.

The lungs, _lu_, and trachea, _ta_, which are now fully formed, are
dissected loose and drawn over to the right side of the animal, together
with the heart, _ht_, and the thymus, _ty_; only one side of the thymus
is shown, the other half being hidden by the trachea.

The mouth has reached nearly the outline of the adult. The lips are
formed and, in the anterior part of the lower jaw, four tooth rudiments,
_to_, are externally visible. The mucous membrane of the roof of the
mouth, _m_, is covered with rounded papillae, easily seen with a lens
but not shown in the figure. The tongue, _tn_, is fully formed, and is
free anteriorly and laterally to about the extent that is seen in the
adult; the papillae with which it is covered are not so prominent as
those seen on the roof of the mouth. At the base of the tongue is the
prominent transverse fold, noted in connection with figure 7, that meets
abo