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PI. V. fig. 2). It is seen from the right side. At o v is the 
orifice of the generative and aquiferous systems, and at x that 
which leads into the pleural sac (“ poche p6riph6rique ”), p s. 
At the posterior part of this sac is seen the slit y, by which it 
communicates with the glandular sac (“ poche centrale ”), g s. 
Anteriorly, at s, is the opening by which the latter sac in its 
turn communicates with the pericardium, p, which invests the 
ventricle of the heart, h, and that portion of the intestine which 
passes through it. At p a the posterior adductor is represented 
in section, and in front of it are seen the culs de sac, which are 
formed by the reflection of the 11 organ of Bojanus ” over it 
dorsally and ventrally. 
Fig. 5 is a kind of ground plan of the u organ of Bojanus.” 
At the anterior part is seen the wide communication, wanting 
in TJnio margaritifer , between the pleural sac of either side, p s , 
p s, and its fellow. Between the sacs lies the venous sinus, 
v s. The rest of the letters have the same signification as they 
have in fig. 4. 
Fig. 6 is a modification of a figure (13) in Professor Huxley’s Elements of 
Comparative Anatomy. It is a diagrammatic representation of 
a vertical transverse section through an Anodon : H u, Mantle- 
lobes ; o g, i g, outer and inner gills respectively ; v, ventricle ; 
and a v , auricle of the heart ; i, intestine in section. The 
remaining letters have the same meaning as they have in previous 
figures. 
Fig. 7 is a plan of the nerve system of the river-mussel. At l g is seen the 
left labial ganglion, which is joined to its fellow by a nerve 
cord. From each labial ganglion are seen to pass, in addition, 
the following nerves : — A branch running straight forwards to 
the anterior adductor, and another backwards to join the 
bilobed branchial, or 11 parieto-splanchnic ” ganglion, b g; a cord 
passing down vertically to the pedal ganglion p g, while another 
runs outward to ramify over the anterior portion of the mantle- 
lobe. 
From the pedal ganglion are given off branches — only a few of 
which are represented in the figure — to the auditory organs 
and foot ; from the parieto-splanchnic ganglion passes back- 
ward on either side a nerve to the rudimentary siphon, while 
outwards run branches to the gills and posterior part of the 
mantle lobe. 
The line of dots indicates a communication, wanting in 
Anodonta , but present in the marine mussel ( Mytilus ), between 
the anterior and posterior pallial nerves. 
Owing to want of space, onty part of the pallial nerves on the 
right side has been figured. Their course is, however, similar to 
that seen on the left side. 
