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MESSRS. F. M. BALFOUR AND W. N. PARKER ON THE 
As we hope to show, this chamber soon becomes largely filled by a vascular 
glomerulus. On the accomplishment of these changes, the pronephros is essentially 
provided with all the parts typically present in a segment of the mesonephros (woodcut, 
fig. 4). There is a peritoneal tube (/.),'* opening into a vesicle (v .); from near the 
neck of the peritoneal tube there comes off a convoluted tube ( pr.n.), forming the main 
mass of the pronephros, and ending in the segmental duct {sd.). 
Fig. 4, 
Diagrammatic views of the pronephros of Lepndosteus. 
A, pronephros supposed to he isolated and seen from the side; B, section through the vesicle of the 
pronephros and the ciliated peritoneal funnel leading into it; pr.n., coiled tube of pronephros; sd., 
segmental or archinephric duct; f., peritoneal funnel; v., vesicle of pronephros; hv., blood vessel of 
glomerulus; gl., glomerulus. 
The different parts do not, however, appear to have the same morphological significance 
as those in the mesonephros. 
Judging from the analogy of Teleostei, the embryonic structure of whose pronephros 
is strikingly similar to that of Lepidosteus, the two pronephric chambers into which 
the segmental ducts open are constricted off sections of the body-cavity. 
With the formation of the convoluted duct opening into the isolated section of 
* We feel fairly confident that there is only one pronephric opening on each side, though we have no 
single series of sections sufficiently complete to demonstrate this fact with absolute certaintv. 
