RENAL ORGANS AND THE URETER. 
335 
In the Euthyiieures there is also but a single kidney, the representa- 
tive of the right kidney of the hypothetical primitive mollusca and 
of the Pelecypod ; it is placed upon the 
roof and in the rear of the pulmonary 
chamber, between the pericardium and 
the rectum and is of the parenchymatous 
type, the complex folds and lamellse of 
the walls projecting into the cavitj" and 
often quite filling up the lumen of the organ. 
The Ureter is the ciliated thin- walled excretory dnct of the kidneys; 
it is paired in the Pelecypoda in correspondence with the paired 
glandular sections whose products they discharge, their apertures 
being usually placed above the base of the foot and opening into the 
supra-branchial or cloacal chambers, in close vicinity to or in con- 
junction with the reproductorj" orifice. 
The duct of each kidney is folded back upon the secretory section 
and are separated by the Vena-cava, but they usually communicate 
by means of the oval inter-renal space near their outlets ; they 
represent the Primary Ureter of the Gastropoda. 
In those species which retain their primitive organization the genital 
glands having no special ducts discharge their products into the 
nephridia, which are transmitted to the exterior by the ureter. 
In our Streptoneura the kidney is placed at the rear of the mantle 
cavity, the slit-like excretory aperture, which characterizes many of 
the groups, opening directly into the pallial cavity, although in 
Vivipara and Valvata the orifice becomes a tubular and elongated 
duct, which is distinguished as the Primary Ureter, a name applied to 
the first direct excretory tract originating at the kidney, and dis- 
charging the waste matters towards the exterior. 
In the Euthyneures the urinary duct has a more complex develop- 
ment and the various stages are to be observed leading from a simple 
aperture, opening directly into the pallial chamber, to a long and 
almost sinuous duct, conveying the renal secretions quite to the 
exterior of the body. 
The Primary Ureter or renal efferent duct is represented by a 
simple orifice in certain species of Planorhis, but is well developed 
and prolonged towards the pulmonary orifice in most other Basom- 
matophora, in Cionella, Pupa, BuUminus and some of the more 
primitive Helices, or, instead of extending directly towards the 
Fig. 623. — Longitudinal section 
through the kidney of A^'iolimax 
a^^restis L., X 50, showing its com- 
plicated structure (after Hanitsch). 
