WOLFFIAN DUCT AND BODY IN THE CHICK, 433 
to the peritoneal epithelium at certain intervals by short cords 
of cells. 
In a chick with twelve protovertebre the separation of the 
Wolffian duct from the intermediate cell mass in the region of the 
7th to the 11th protovertebre inclusive is as complete as it ever 
will be, z.e. it has separated for the greater part of its length, but 
remains attached to the peritoneal epithelium at certain points, 
by cords of cells (fig. 2) derived from the cells of the inter- 
mediate cell mass connecting the rudiment of the Wolffian duct 
with the peritoneal epithelium. ‘These cords of cells are the 
commencing Wolffian tubules of the anterior part of the Wolffian 
body, and are more numerous than the segments in which they 
are placed. Behind the region of the protovertebre in a chick 
of this age (twelve protovertebre), the Wolffian duct has grown 
back as an irregular cord of cells (fig. 6), independent of the 
intermediate cell mass, for a short distance, thus repeating the 
feature of the last and succeeding stages in this particular. In 
the region of the last (12th) protovertebra, however, the cord of 
cells constituting the Wolffian duct at this stage is now con- 
tinuous with the intermediate cell mass at certain intervals. 
Comparing the sections through the 12th segment of this stage 
with those just behind the 11th protovertebra of the previous 
stage, it is seen that the Wolffian duct has enlarged, and by a 
downgrowth of cells from it, with which probably is connected 
an upgrowth from the intermediate cell mass, has become in 
certain places connected with the intermediate cell mass. These 
secondary connections constitute the commencing tubules of this 
part of the Wolffian body. 
In a chick with thirteen protovertebree an advance precisely 
similar to that characterising the previous stage has taken place, 
i.e. the Wolffian duct has become connected with the inter- 
mediate cell mass in the 13th segment (fig. 7), and behind 
this point is free from adjacent structures. 
In a chick with fourteen or fifteen protovertebre the process 
of development remains the same. So that im a chick with 
fifteen segments the following is the condition of the Wolffian 
duct :—It extends from the 7th to the 15th segment as a solid 
cord of cells, connected at intervals with the peritoneal epithe- 
lium by the commencing Wolffian tubules; behind the 15th 
segment it extends for a short distance asa free cord. The further 
development differs from that just recorded in this important 
particular ; the duct does not become connected with the inter- 
mediate cell mass of the newly-formed last segment, but remains 
separate for a considerable interval of time (till towards the end 
of the third day) from it. In other words, the formation of 
