WOLFFIAN DUCT AND BODY IN THE CHICK, 435 
12th—15th segments inclusive ; (3) that found behind the 15th 
segment. 
In a previous paper! I have described at some length the 
early development of the Wolffian body behind the 16th segment, 
and I have there shown that that part may be divided into two 
parts, each characterised by a peculiarity in the early develop- 
ment. In this paper I shall make but little reference to the 
development of the Wolffian body in this region, confining 
myself almost entirely to that part lying within the area of the 
7th to the 15th segments inclusive. 
Development of Wolffian Tubules in region of 1th—11th 
Segments. 
The Wolffian tubules and Wolffian duct in this region attain 
but a slight development. They may almost be said to have 
reached their highest point at the stage with fourteen proto- 
vertebre, the only difference in later stages being the develop- 
ment of a lumen in them. The lumen in the tubule may 
acquire an opening into the Wolffian duct in some cases. In 
this case the string of cells seen in fig. 5 becomes very short, 
and the Wolffian duct appears as a narrow groove in the peri- 
toneal epithelium. This state of things is usually found in 
chicks with from nineteen to thirty-two protovertebre. 
The Wolffian duct in this region exhibits great variations in 
calibre, and in later stages parts of it appear to atrophy, and 
isolated portions are found connected with rudimentary tubules. 
An enlarged section of the Wolffian duct in front is nearly 
always found as Gasser® has described. The duct and tubules 
in this region appear entirely to atrophy in chicks with more than 
thirty-five protovertebre. 
I have not thought it worth while to preserve figures of the 
duct and tubules in this region of the Wolffian body after their 
first appearance, as the arrangement just described may be easily 
observed in sections of an embryo chick of the third day. 
The interest in the development of this region lies in the fact 
of the continuity of development of the Wolffian tubules and 
Wolffian duct. It has always appeared to me astonishing that 
the Wolffian duct developed as a continuous ridge from the inter- 
mediate cell mass, which, from our knowledge of Elasmobranch 
development, may be called the peritoneal epithelium, should 
entirely separate from it and then secondarily become connected 
with it by the tubules of the Wolffian body. My investigations, 
which have been made with some care on a large number of 
I Loe. cit. 2 Loc. cit. 
