BY JAS. P. HILL AND C. J. MARTIN. 
63 
while a short distance further forward a single distinct lumen 
occurs, but it is confined to one section. Apparently we have 
here to do with the last traces of the notochordal canal. 
The head process diminishes in thickness anteriorly and finally 
passes into the posterior end of the notochord. 
Wolffian duct and body : The appearance of the Anlagen of the 
Wolffian duct and body has already been described in surface 
view. In sections of its anterior region from the 4th to the 7 th 
somites the united Anlagen of the Wolffian duct and body appear- 
as a solid cord of cells projecting from the intermediate cell mass. 
The greater part of the cord lies free between the outer edges of 
the somites and the lateral mesoderm, while its dorsal surface 
approaches within a short distance of the ectoderm (fig. 8, id. b.). 
As the cord is traced backwards it is found to become gradually 
constricted in its middle region, while its dorsal portion broadens 
out, until it becomes somewhat dumb-bell-shaped in form. Its 
basal portion is now very distinctly connected with the lateral 
mesoderm on its outer side. On its inner side, however, the 
connection with the somites is not now so well marked, and in 
places this connection is completely lost. At about the level of 
the 6th somite the constriction of the middle region of the cord 
is much more marked, and it here consists of a ventral larger 
rounded mass connected by a narrow isthmus with a dorsal much 
thinner flattened band. The upper portion is the Anlage of the 
Wolffian duct, while the lower is the Anlage of the Wolffian 
tubules. Then, by the gradual disappearance of the connecting 
isthmus the mass comes to consist of a dorsal band-like Wolffian 
duct Anlage (fig. 25, w.a.), united at its mid-region to the under- 
lying Anlage of the tubules (w.t. ). Finally, opposite the 7th 
somite the narrow connection between the duct Anlage and the 
Anlage of the tubules is lost altogether, and the two become 
separate (fig. 26). 
The outer edges of the duct Anlage lie close below the ectoderm 
which, just over the duct, is very thin and delicate, and with very 
few nuclei as compared with the rest of the ectoderm. Very 
