438. ADAM SEDGWICK. 
mesentery varies in thickness in different sections, but we believe 
that the glomerulus is continued unbroken throughout the very 
considerable region through which it extends. This point is, 
however, difficult to make sure of, owing to the facility with 
which the glomerulus breaks away. At the stage we are 
describing no true Malpighian bodies are present in the part of 
the Wolffian body on the same level with the anterior end of the 
glomerulus, but the Wolffian body merely consists of the Wolffian 
duct. At the level of the posterior part of the glomerulus this 
is no longer the case, but here a regular series of primary Mal- 
pighian bodies is present, and the glomerulus of the head-kidney 
may frequently be seen in the same section as a Malpighian 
body. In most sections the two bodies appear quite discon- 
nected, but in those sections in which the glomerulus of the 
Malpighian body comes into view it is seen to be derived from 
the same formation as the glomerulus of the head-kidney.” 
The point which is left in doubt in the above description, 
viz. as to whether the glomerulus constitutes a continuous 
structure, is at once decided by a study of its development. 
I may here state that it is not a continuous structure, but 
consists of a series of external glomeruli, each of which corre- 
sponds and is continuous with the glomeruli of the Malpighian 
bodies found in this part of the trunk. 
The first development of the Wolffian tubules in the region 
under consideration has already been described. They appear 
as outgrowths from the Wolffian duct meeting outgrowths from 
the intermediate cell mass immediately on the formation of the 
segment in which they are placed ; so that in a chick with fifteen 
protovertebree the Wolffian duct is connected with the inter- 
mediate cell mass by a certain number of cell cords in the 12th, 
13th, 14th, and 15th segments. ; 
The duct and cords, which have at first rather an irregular 
outline, soon become well-defined compact structures. 
Fig. 12, taken from the 12th segment of an embryo with 
twenty-two segments, represents the condition of things at this 
age. 
The Wolffian tubules in this region are derived from two 
distinct structures—(1) the outgrowth from the Wolffian duct ; 
(2) part of the intermediate cell mass. 
The intermediate cell mass is at first continuous with the 
peritoneal epithelium in every section; but, as described in a 
previous paper, this connection soon becomes lost at certain 
points (fig. 9), and maintained at others (fig. 10). Figs. 9 and 
10 are contiguous sections through the 15th segment of a chick 
with twenty-two segments, showing this point. At these points, 
where the continuity is retained, a peritoneal funnel is subse- 
