RENAL ORGANS. 
883 
Fig. 618 .— Kidney cells of Helix 
arbustofum L. , highly magnified, 
showing the contained Uric acid 
concretions (after Boll). 
yellowish tissue, containing nninerons ca'ca and projecting glandnlar 
lamellre or trabecnloe, overspread by a densely ciliate la3"er of secretor}' 
cells, wbicb fill np the lumen of the organ and contain a yellowish or 
greenish Hnid with concentrically formed 
concretions, similar to those in the renal 
organs of other animals, the rupture of 
the cell-walls allowing their escape. 
The deoxidized and impure blood re- 
turning from its circuit of the body, 
laden with the waste products of the 
oxidation of the tissues, joins with some arterial blood from the lung 
and circulates within the kidnej'S before reaching the respiratory 
organs, thus constituting a portal circulation which partially purifies 
the blood by eliminating therefrom the nitrogenous waste matters, in 
the form of Urea, Uric Acid, Galcium-phosphate and other substances, 
amongst which Ammonia, Creatinin, Tyrosin, Leucosin, (fuauin, etc., 
have been recorded. 
The excretory substances vary somewhat in character in the different 
groups, the Pelecypoda chiefly expelling Urea, which is formed by 
the more or less complete oxidation of the anatomical elements of 
muscular tissue and is produced most plentifully during periods of 
abstinence or food scarcity ; while manj' Streptoneures excrete Uric 
acid, which results from an 
incomplete oxidation, due to 
the blood being surcharged 
with pe[)tones which the 
tissues are unable to assimi- 
late, a state consequent upon 
a plethora of food. 
In the Pelecypoda the 
kidneys are known as the 
Organ of Bojanus, the 
simplest form being found 
in Nucula and other Proto- 
branchiates, in which they 
consist simply of a pair of 
folded and separate cylindrical sacs, placed beneath the pericardium 
and in front of the posterior adductor, each sac possessing a .spacious 
lumen and similar secretoiy walls throughout its extent, the pericardial 
Fig. 619. — Diagram formed from several combined 
transverse sections through Anodonfa, showing the 
relative positions of the kidneys or renal organs and 
their ducts (after Griesbach). 
n. nephridia, with r./. reno-pericardial funnels and 
7i. ureters ; pc. pericardium ; n. auricle ; v. ventricle ; 
s. vena-cava or blood-sinus ; r. rectum ; g. genital 
ducts. 
