WOLFFIAN DUCT AND BODY IN THE CHICK, 441 
cavity. This is at once clear on inspection of figs. 16, 17, 18. 
These figures are taken from the 13th segment of a chick with 
thirty-four protovertebre. There was a section not figured 
between fig. 17 and 18, otherwise the sections are successive, 
fig. 16 being the anterior. 
Tn fig. 16 is seen the commencement of the peritoneal funnel 
as a bay lying between the Wolffian duct and mesentery. 
In fig. 17, a glomerulus (g/.) has appeared projecting into this 
bay. In the next section, not figured, the bay was almost 
closed up by an approximation of its edges, while in fig. 18 the 
bay is completely shut off from the body cavity, and we have a 
section of a true Malpighian body with its contained glomerulus. 
Fig. 18 clearly corresponds to fig. 15 of the previous stage, 
while fig. 17 corresponds to fig. 14, the difference being that a 
distinct cellular projection (g/.) has appeared at the point where 
the projection of cells from the Wolffian duct joins the inter- 
mediate cell mass. 
I have given a diagram (fig. 22) representing an ideal longi- 
tudinal dorso-ventral section through two of these Wolffian 
tubules at this stage. This diagram has been made from a study 
of many embryos showing the development of the external 
glomerulus. 
The open peritoneal funnel is represented at p. 7, the arrow 
pointing into it. Through it is projecting the anterior part of 
the glomerulus (g/.), that part which I shall call the external 
glomerulus. A transverse section through this part would 
give the appearance represented in fig. 17. 
Into the closed hinder part of the tubule (mé.) is projecting 
the hinder part of the glomerulus (2. g/.), which I shall call the 
internal glomerulus. It was. not possible to represent satis- 
factorily in this diagram the Wolffian duct, which, obviously 
from its position in transverse section, would not be seen in a 
longitudinal section passing through the attachment of the 
glomerulus. 
In fig. 23 is represented somewhat diagrammatically a trans- 
verse section through a chick with thirty-three protovertebre, 
i.e. from a slightly younger embyro than that from which 
figs. 16—18 were taken, in which the cord of cells connecting 
the Wolffian duct with the cavity of the glomerulus had acquired 
a distinct lumen, the cavity of the Wolffian duct being here 
distinctly continuous with that of the bay in which is placed 
the rudimentary external glomerulus, and so with the body 
cavity. At subsequent stages this part of the tubule appears to 
persist, but only in a rudimentary fashion. 
The next stage which I propose to describe was found in a 
