442 ADAM SEDGWICK. 
chick in which thirty-six protovertebre could be counted, but 
possibly there were more. 
The glomerulus has grown immensely (figs. 19, 20, 21), and 
has now acquired the peculiar histological features which 
characterise it at the time of its greatest development, and which 
have already been described in a former paper. 
Anteriorly the bay has widened out considerably (fig. 19), 
and the glomerulus (e. g/.) projects directly into the body 
cavity. Posteriorly the bay remains deep (figs. 20, 21), and the 
glomerulus almost completely fills it and projects beyond it into 
the body cavity. In sections behind fig. 21 there was seen a 
fairly well-developed internal glomerulus. 
The edges of the bay are gathering round the glomerulus pre- 
paratory to fusing with it, and so closing up the peritoneal 
funnel and dividing the glomerulus completely into two parts, 
the internal vascular tissues of which, however, are continuous. 
In this stage the epithelial covering of the external glomerulus 
(ce. gi.) was distinctly, as in the previous stage, continued behind 
directly into that covering the posterior internal glomerulus. 
When, however, the peritoneal funnel closes by the comple- 
tion of the process commencing in figs. 20 and 21, this epithelial 
continuity is lost, and we have the final stage of the glomerulus, 
the last which I have observed, in which the separation above 
described is complete, so that in this stage, which is that of the 
greatest development of the external glomerulus, and corre- 
sponds with the commencing formation of the head-kidney, the 
glomerulus belonging to one tubule is divided into three parts. 
(1) An anterior! part projecting into the body cavity. ‘This 
corresponds to a further development of fig. 19. 
(2) A middle part, continuous with (1), also projecting 
freely into the body cavity, but also connected by vascular 
structures with an internal glomerulus. This part is figured in 
fig. 26, and corresponds to a further development of the part 
from which fig. 20 and 21 were taken. 
(3) A posterior part, in which there is no external glomerulus, 
but merely an internal one belonging to a true Malpighian 
body of the mesonephros, which I have not thought it neces- 
sary to figure in this or the previous stage. It is a further 
development of fig. 18. This stage, which may be observed 
about the middle of the fourth day of incubation, brings to a 
close my observations on this extraordinary structure. It appears 
that in the chick the stage just described is that of the greatest 
development of the external glomerulus. In the duck, however, 
T have often met with it even larger and more developed, and 
\ Fig. E, Pl. Il, in the paper on the “ Head-Kidney of the Chick,” 
* Quart. Journ. Mic. Sci.,’ vol. xix. 
