450 ADAM SEDGWICK. 
in my sections of the Frog, but have completely failed to 
find the earlier stages of this ingrowth. One would expect to 
see it preceded by a thickening of the very flat cells lining the 
body cavity at this point; one would hardly expect the flat 
cells so specialised to form the lining of the body cavity of 
the young larva suddenly, and without showing any change to 
begin to grow inward. Further, if the cell cords described by 
Fiirbringer in the Salamander are really only rudimentary struc- 
tures belonging to the anterior part of the mesonephros, as is 
certainly the case in the Frog; and if the process which Fiir- 
bringer describes for the posterior part of the mesonephros of 
the Salamander takes place for all fully-developed parts of the 
mesonephros, as is the case in the Frog, then part of the diffi- 
culty caused by the peculiar secondary development of the 
peritoneal funnels disappears. In other words, I believe Fur- 
bringer has made a mistake, precisely similar to that which was 
made about the development of the Avian Wolffian body. He 
has seen in the anterior part of a young larva the cell cords 
mentioned above ; which were present at a time when there was 
no trace of the posterior part of the mesonephros. He has also 
seen in the hinder part of older larve the blastema of cells 
separate from the peritoneal epithelium from which the Wolffian 
tubules arise. Finally, he has connected these two conditions, 
which are, as I believe, found in different regions of the trunk, 
and has concluded that the cell strings of the anterior part have 
separated from the peritoneal epithelium and given rise to the 
cell masses of the posterior part which really develop indepen- 
dently of the peritoneal epithelium, and eventually give rise to 
the Wolffian tubules. 
My observations on Teleostei lead me, for similar reasons, to 
assert an origin, im sité, of a continuous blastema, which later, 
breaking up, will give rise to the Wolffian tubules. 
On the other hand, the older observers, including Vogt and 
Rosenberg for Teleostei, Rathke, Johan. Miiller, Reichert, Vogt, 
for Amphibia,” are quoted by Fiirbringer as asserting an origin 
of the tubules as a series of excavations in a blastema of cells 
lying just internal to the segmental (Wolffian) duct. And it 
seems to me that the older observers were,® as in their state- 
ments concerning the development of the mesonephros in the 
chick, not far from the truth. In the Sturgeon my observations 
point to a similar conclusion; in the just-hatched young a few 
mesoblast cells are seen lying internal to the segmental duct. 
These, at a later stage, are replaced by a more compact mass of 
1 © Firbringer,’ loc. cit., p. 46. 
2 Ibid., loc. eit., p. 12. 
3 Self, ‘ Quart. Journ. Mic. Sci.,’ April, 1880. 
