434: ADAM SEDGWICK. 
the Wolffian tubules and their connection with the Wolffian 
duct is deferred behind the 15th segment. 
To sum up the developmental changes above recorded, the 
Wolffian duct arises as a continuous ridge of cells projecting 
from the intermediate cell mass towards the epiblast in the 
region of the 7th to 11th protovertebre inclusive. This ridge 
separates from the intermediate cell mass from before backwards, 
remaining, however, connected with it at intervals by the rudi- 
mentary Wolffian tubules. Meanwhile, from the hind end of it 
there grows back a cord of cells independent at first of the 
adjacent structures, but immediately on the formation of the 
hinder segments becoming connected with the intermediate 
cell mass of each segment in turn. This happens as far. back 
as the 15th segment; behind this point it grows back as a 
solid cord, which does not become connected with the inter- 
_mediate cell mass until the tubules of the Wolffian body have 
made considerable advance in their development. 
Figs. 1—7 are meant to illustrate the above method of develop- 
ment. Figs. 1—5 are from the 10th segment of chicks, with 
ten, twelve, thirteen, and fourteen protovertebre respectively. 
They are all taken through points where the Wolffian duct remains 
attached to the peritoneal epithelium, z.e. through a rudimentary 
tubule, excepting fig. 4, which is from a section close to fig. 3, 
and shows the condition of things in one of the intervals between 
the points of continuity. 
Fig. 6 is taken from a section just behind the last segment of 
a chick with twelve segments, and shows the complete inde- 
pendence of the Wolffian duct. 
Fig. 7 is from the 13th segment of a chick with thirteen seg- 
ments, 7.e. from the same region as fig. 6, and it shows the con- 
nection which has become established between the Wolffian 
duct and the intermediate cell mass by a mutual growth of these 
structures. val 
Fig. 8 is from the 16th segment of a chick with twenty-two 
protovertebre, and is illustrative of the fact derived from an 
inspection of all the sections of the segment, that the Wolffian 
duct is independent of the peritoneal epithelium. From the 
15th segment the Wolffian duct grows back independently to 
the cloaca, into which it eventually opens, and a lumen appears 
in it from before backwards. 
In fig. 11, taken from a chick at the end of the third day, it 
is still distinct from the now considerably developed Wolffian 
tubule (w.?.). 
For purposes of description I shall divide the Wolffian body 
into three regions—(1) The part found within the limits of the 
7th—11th segments inclusive ; (2) the part found within the 
