WOLFFIAN DUCT AND BODY IN THE CHICK. 449 
As the mesonephros becomes more developed the pronephros 
retrogrades, and: is eventually entirely, as far as its function is 
concerned, replaced by the former. 
The development of the mesonephros in Teleostei, Marsi- 
pobranchii, Ganoidei, is similary described as taking place in the 
free young (larva) from strings of cells derived from the peri- 
toneal epithelium. In Marsipobranchii as in Amphibia the young 
are hatched with a functional pronephros, and no trace of the 
mesonephros; but the former is, in the further growth of the 
young animal, gradually replaced functionally by the latter, and 
more or less retrogrades. In the Teleostei, however, and 
Ganoidei, it persists with the mesonephros as an important 
functional organ in the adult. In some Teleostei the pronephros 
is the only functional aduit kidney, the mesonephros not being 
developed. 
I have made some observations on the development of the 
mesonephros in the Frog (Rana temporaria), Salmon and Stur- 
geon, and my observations lead me very strongly to doubt whether 
Fiirbringer and other observers are right in describing the origin 
of the cells which give rise to the mesonephros as actual 
ingrowths from the peritoneal epithelium. 
In the case of the Frog this is certainly not the case. In 
fig. 25 is represented a section through a Tadpole of 11 mm., 
showing the first trace of the cells (k B) from which the Wolffian 
tubules arise. At their first appearance they are independent 
of the peritoneum, and only secondarily become connected 
with it. Fiirbringer figures from the Salamander a section 
in support of his statement ; I have also seen such appearances 
in the Tadpole, but in this animal these strings are only found 
in that part of the animal in which, I am confidently able to state, 
no Wolffian tubules are ever developed. I have examined and 
compared segment with segment of Tadpoles of various ages, 
and have never found these strings of cells developing into 
Wolffian tubules. The cell strings appear to me to arise from a 
blastema of cells developed zm sitd becoming connected with the 
peritoneal epithelium, and they are, no doubt, rudimentary 
tubules. 
Fiirbringer in his paper gives no evidence of the origin of 
these cells from the peritoneal epithelium, except a drawing of 
a stage in which the blastema is connected with the peritoneal 
epithelium.’ I have also seen this stage, as mentioned above, 
' Gotte also, in his latest writings on the subject, agrees with Fiirbringer 
as to the origin of the cells which give rise to the mesonephros. But 1 may 
draw attention to the fact that Gotte has held three views on this point, 
the last of which did not appear (see Firbringer, loc. cit.) till 1875, i.e. 
after the publication of Balfour and Semper’s works on ‘ Elasmobranchi,’ 
