.162 
ADAM SEDGWICK. 
3. Wolffian tubules do not appear in any part of the blas- 
tema behind the thirtieth segment. Primary, secondary, and 
tertiary, &c., tubules are developed in that part of it placed 
in the thirtieth and anterior segments as far as the twenty- 
first or twenty-second, and primary tubules in yet anterior 
segments. 
4. The blastema in the thirty-first to thirty-fourth segments, 
on the appearance of the ureter, moves dorsalwards from the 
Wolffian duct, breaking away from the hindermost Wolffian 
tubules and enters into close relation with the ureter. 
5. This part of the blastema — the kidney blastema — espe- 
cially collects round swellings on the ureter, from which 
kidney tubules grow out. 
6. These kidney tubules burrow into the kidney blastema, 
their growing points being continuous with the cells of the 
blastema. 
Five years ago Balfour ^ and Semper ^ independently put 
forward the hypothesis that the kidney of the Amniota holds 
the same relation to the embryonic Wolffian body as does the 
adult kidney in Elasmobranchs. 
Balfour wrote then The last feature in the anatomy of 
the Selachians which requires notice is the division of the 
kidney into two portions, an anterior and posterior. The 
anatomical similarity between this arrangement and that of 
higher Vertebrates (birds, &c.) is very striking. The anterior 
one precisely corresponds, anatomically, to the Wolffian body, 
and the posterior to the true permanent kidney of higher 
Vertebrates ; and when we find that in the Selachians the 
duct for the anterior serves also for the semen, as does the 
duct of higher Vertebrates, this similarity seems almost to 
amount to identity.’’ 
The development of the kidney of the bird has never 
been fully w'orked out, so that this hypothesis, arrived at from 
a consideration of the facts of comparative anatomy and Elas- 
mobranch embryology, has hitherto not been tested by the 
facts of Avian embryology. The observations described above 
were undertaken with a view of testing this hypothesis, and, 
in my opinion, it has fully stood the test. 
The development of the kidney in the chick points most 
decidedly to the conclusion that it is merely the posterior 
part of the Wolffian body — or, perhaps, it would be better to 
say, of a primitive organ, the anterior part of which is now 
^ “Urogenital Organs of Vertebrates/’ ‘Journal of Anatomy and 
Physiology/ vol. x, 
2 Loc. cit. 
3 P. 27. 
