420 
MESSRS. F. M. BALFOUR ARD W. R. PARffER OR THE 
III. — 'Theoretical considerations. 
There are three points in our observations on the urinogenital system which appear 
to call for special remark. The first of these concerns the structure and fate of the 
pronephros, the second the nature of the oviduct, and the third the presence of vasa 
eflferentia in the male. 
Although the history we have been able to give of the pronephros is not complete, 
we have nevertheless shown that in most points it is essentially similar to the 
pronephros of Teleostei. In an early stage we find the pronephros provided with a 
peritoneal funnel opening into the body-cavity. At a later stage we find that there is 
connected with the pronephros on each side, a cavity—the pronephric cavity—into 
which a glomerulus projects. This cavity is in communication on the one hand with 
the lumen of the coiled tube which forms the main mass of the pronephros, and on 
the other hand with the body-cavity by means of a richly ciliated canal (woodcut, 
fig. 4, p. 416). 
In Teleostei the pronephros has precisely the same characters, except that the cavity 
in which the glomerulus is placed is without a peritoneal canal. 
The questions which naturally arise in connexion with the pronephros are : (1) what 
is the origin of the above cavity with its glomerulus; and (2) what is the meaning of 
the ciliated canal connecting this cavity with the peritoneal cavity'? 
We have not from our researches been able to answer the first of these questions. 
In Teleostei, however, the origin of this cavity has been studied by Rosenberg* and 
GoTTE.t According to the account of the latter, wdiich we have not ourselves confirmed 
but wdiich has usually been accepted, the front end of the segmental duct, instead of 
becoming folded off from the body-cavity, becomes included in a kind of diverticulum 
of the body-cavity, which only communicates with the remainder of the body-cavity by 
a narrow opening. On the inner w^all of this diverticulum a projection is formed which 
becomes a glomerulus. At this stage in the development of the pronephros we have 
essentially the same parts as in the fully formed pronephros of Lepidosteus, the only 
difference being that the passage connecting the diverticulum containing the glomerulus 
with the remainder of the body-cavity is short in Teleostei, and in Lepiclosteus forms a 
longish ciliated canal. In Teleostei the opening into the body-cavity becomes soon 
closed. If the above comparison is justified, and if the development of these parts in 
Lepidosteus takes place as it is described as doing in Teleostei, there can, we think, be 
no doubt that the ciliated canal of Lepidosteus, wdiich connects the pronephric cavity 
with the body-cavity, is a persisting communication between this cavity and the 
body-cavity; and that Lepidosteus presents in this respect a more primitive type of 
pronephros than Teleostei. 
It may be noted that in Lepidosteus the whole pronephros has exactly the character 
of a single segmental tube of the mesonephros. The pronephric cavity with its 
* Rosenberg, Untersiicb. lib. d. Entwick. d. Teleostierniere. Dorpat, 1867. 
f Gotte, Entwick. cl. Unke, p. 826. 
