154 
ADAM SEDGWICK. 
(fig. 1^) are continued as small channels in the intermediate 
cell mass or Wolffian blastema, and remain, enlarging when 
the Wolffian tubules are formed later, I have been unable to 
ascertain. Neither have I been able to satisfy myself as to 
another interesting point, viz. Do those rudimentary nephro- 
stomata correspond to the Wolffian tubules subsequently 
developed? In the chick’s twentieth segment never more 
than three, at the most, nephrostomata can be made out, 
yet there are four or five primary Wolffian tubules later. 
Has this increase been caused by the development of more 
tubules than there were nephrosomata, e, by intercalation, 
or has it been caused by a change in the relation of the parts 
to one another, due either to an elongation of the proto- 
vertebra or to the travelling forward of the tubules as they 
are developed behind ? 
I shall return to the consideration of this point in a future 
paper. 
The mode in which the Wolffian blastema behind the 
twentieth^ segment breaks up into tubules, so far as I have 
been able to ascertain it, is the following : — A number of 
vesicles, either oval or circular, lined by columnar cells, and 
lying just internal to the Wolffian duct, make their appear- 
ance (fig. 5). In longitudinal sections it may be seen that 
these vesicles closely adjoin one another antero-posteriorly. 
They are developed from those cells of the Wolffian blastema 
immediately adjoining the inner border of the Wolffian duct. 
By a study of transverse sections it appears that each vesicle 
is continuous ventrally with that part of the Wolffian blas- 
tema which has not undergone conversion into the walls of 
the vesicle, and which dies just internal to the vesicle. The 
cells of this part of the Wolffian blastema very soon arrange 
themselves round what appears as a continuation of the 
original vesicle (fig. II). From the inner and dorsal wall 
of the last-formed structure a glomerulus is ultimately de- 
veloped. The whole structure grows enormously, and gives 
rise to the Malpighian body and complicated coils of the 
later Wolffian tubule. At about the stage of development 
represented in fig. 11 the tubules acquire an opening into 
the Wolffian duct. 
The question as to whether or no there are outgrowths 
from the Wolffian duct to meet the independently developed 
^ Vide also fig. 125, of Kolliker’s ‘ Entwick. gesch. der Menschen u. 
der. h. Thiere.’ 
^ I reserve an account of the development of the tubules in front of the 
twentieth segment, as my observations on this point are not yet suffi- 
ciently complete to enable me to speak with certainty. 
