EXCRETORY SYSTEM. 409 
Excretory system.—The excretory system is difficult to dissect and 
to explain. On each side of the anus there is a little papilla, through 
which uric acid and other waste products ooze out into the mantle 
cavity, and so into the water. A bristle inserted into either of these 
two papillz leads into a large sac—the nephridial sac. But the two 
sacs are united by two bridges, and they give off an unpaired dorsal 
elongation, which extends as far back as the reproductive organs. 
The dorsal wall of each nephridial sac becomes intimately associated 
with the branchial veins, and follows their outlines faithfully. It is 
likely that waste material passes from the blood through the spongy 
appendices into the nephridial sacs. 
Fic, 219.—Diagram of circulatory and excretory systems 
in a Decapod-like Sefza.—After Pelseneer. 
x, Gill; 2, renal sac; 3, afferent branchial vessel; 4, branchial heart ; 
5, abdominal vein; 6, heart; 7, viscero-pericardial sac (body 
cavity); 8, genital organ; 9, posterior aorta; 10, “auricle” ; 11, 
glandular appendix of branchial heart; 12, renal appendices of 
branchial vein; 13, external aperture of kidney; 14, vena cava; 
15, anterior aorta; 16, bifurcation of vena cava; 17, reno-pericardial 
aperture, E 
Into the terminal portion of each nephridial sac, a little below its 
aperture at the urinary papilla, there opens by a ciliated funnel another 
sac, which is virtually the body cavity. It surrounds the heart and 
other organs, and is often called the viscero-pericardial cavity. 
Through the kidneys or nephridial sacs it is in communication with the 
exterior. Associated with the branchial hearts there are numerous 
diminutive cells which contain ammoniacal salts, phosphates, pigment, 
etc. ; these waste products are probably passed into the blood and got 
rid off by the kidneys, just as, in 2 Vertebrate, the urea formed in the 
liver passes by the blood to the kidneys. In Invertebrates there 
is often this co-operation between ‘‘closed. kidneys” and ‘‘ open 
kidneys.” 
