THE GASTROPODA 109 
3. Hxcretory Organs.—In the Gastropoda the kidneys are the 
essential organs of excretion, but the pericardial glands serve as 
accessory excretory organs, as also certain parts of the body in 
which the products of excretion are collected, forming veritable 
accumulative kidneys. 
(1) The kidneys are originally paired, as in all other Mollusca, 
and a single pair is found (Figs. 55, III, XIII; 81, f, h; 91, 
127) in all the Aspidobranchia, except the Neritacea, including 
the Neritidae and allied families. These two kidneys open one 
on each side of the anus, but they do not retain their primitive 
symmetry in any Gastropod, and although they are independent of 
one another, the topographically left kidney is rudimentary, and 
that of the right side alone is functional in almost every case. 
See SENS 
ee «ott MANNS 
Reine Sh USA x 
RUDE es 
Wintly GAIN SNe ee 
; ae 
Fic. 90. 
Transverse section of the lung of Janella. k, ureter; pa.c, pallial or pulmonary cavity ; po, 
pneumostome ; si, blood sinus ; tr, ‘‘ tracheae” or diverticula of the pulmonary cavity. (After 
Plate.) 
In the Neritacea (Neritidae, Titiscaniidae, Helicinidae, Hydro- 
cenidae, and Proserpinidae) and in all the Pectinibranchia and 
Euthyneura the topographically right kidney no longer exists. 
In Paludina the two kidneys coexist during development, but in 
the adult that of the topographical right side has disappeared. As 
regards the position of these organs, their primitive situation is 
wholly within the visceral mass (Docoglossa, Fig. 88, i), and their 
migration outside the visceral mass is a specialisation which begins 
to show itself in the Rhipidoglossa—at any rate, in the case of the 
left kidney (Fig. 127)—and is completely realised in the case of the 
single kidney in other Streptoneura and Tectibranchia, in which 
the excretory organ is more and more localised in the mantle (Figs. 
75,k; 63,7). The kidney is always a dorsal organ, situated in the 
neighbourhood of the pericardium, with which it communicates by 
a ciliated aperture. In the detorted Aspidobranchs (Fissurellidae), 
however, the very rudimentary left kidney has lost this pericardial 
