The Shell-Collector’s Handbook. 27 
of Bojanus, and thence by the afferent branchial veins 
to the gills, where it becomes purified, losing carbonic 
anhydride, and gaining oxygen. 
From the gills it is returned by the efferent branchial 
veins to the auricles. A plexus of vessels, known as 
the organ of Keber, exists near where the efferent 
branchial veins open into the auricles ; but its function 
has not yet been demonstrated. The blood from the 
mantle-lobes is returned direct to the heart, and does 
not circulate either through the Organs of Bojanus, 
or the gills. i 
THE OrGANS oF Bosanus.—The Organs of Bojanus 
or the kidneys are two in number, and situated just 
beneath the pericardium. Each will be found, on 
examination, to consist of a glandular, and a non- 
glandular part. The glandular portion communicates 
anteriorily with the pericardial cavity, and posteriorly 
‘with the non-glandular part or vestibule, from whence 
the excretory products are conducted to the exterior 
by a thin walled wreter, which opens by the external 
renal aperture between the two lamelle of the inner 
gill, and just posterior to the external opening of the 
generative gland. Urea and uric acid have been 
recently demonstrated in these organs, and they serve, 
therefore, an excretory function, and correspond to 
the kidneys of the higher animals. 
THe Nervous System.—The nervous system consists 
of three pairs of ganglia—the cerebral, pedal, and the 
osphradial or parieto-splanchnic ganglia. The cerebral 
ganglia are situated one on each side of the mouth, 
and give off labial, pallial, muscular, and anterior 
branchial branches. They correspond to the supra- 
