436 ADAM SEDGWICK. 
chicks of all ages from nine to thirty protovertebre, have 
entirely convinced me that the usual statements on this point are 
not true, and show to my mind most conclusively that the duct 
and tubules of the Wolffian body in the region in question do 
develop in continuity, precisely as do the duct and peritoneal 
openings of the head-kidney in most Ichthyopsidan types. 
The number of rudimentary tubules in each segment of this 
region I have not determined precisely. They occur as often 
as not between the segments, and there seems to be about two for 
each segment. In the seventh segment I have never seen more 
than one. 
Before proceeding to give an account of the further develop- 
ment in the next region, I will briefly refer to the points in 
which my observations differ from those of previous observers 
on the development of the Wolffian duct. 
Gasser’s account of the development of the Wolffian duct is 
the most recent and exact. In his valuable paper will be found 
a complete account of the literature of the subject, to which I 
need not further refer. 
“The first trace of it which he finds is visible in an embryo 
with eight protovertebre as a slight projection from the inter- 
mediate cell mass towards the epiblast in the region of the three 
hindermost protovertebree. In the next stage with eleven pro- 
tovertebre, the solid rudiment of the duct extends from the 5th 
to the llth protovertebre ; from the 8th to the 11th 
protovertebrze it lies between the mesoblast and epiblast, and is 
quite distinct from both, and Dr. Gasser distinctly states that 
in its growth backwards from the 8th protovertebre the 
Wolffian duct never comes into continuity with the adjacent 
layers. In the region of the 5th protovertebraee, where the 
duct, &c., was originally continuous with the mesoblast, it has 
now become free, but is still attached in the region of the 6th 
to the 8th. In an embryo with fourteen protovertebre the 
duct extends from the 4th to the 14th, and is now free between 
epiblast and mesoblast for its whole extent.” 
The points in which the preceding account differs from that 
of Dr. Gasser’s briefly are : 
1. The position of the continuous ridge of the Wolffian duct. 
2. The subsequent complete isolation of the duct in the 
region of the ridge. 
3. The independence of the backward growth of the duct in 
the 12th to the 15th segment. 
I have never seen any trace of the Wolffian duct in front of 
the 7th segment, and in all the chicks I have examined I find 
1 © Arch. fiir Mic. Anat.,’ vol. xiv. 
