’ THE LAMELLIBRANCAIA 269 
S ah ay, 
ay Ul 
a 
“Pag am 
b 4 ‘1 au 
Fic. 242. 
Diagrams of the external form and anatomy of Anodonta cygnaea (2), ventral view, all ,the 
other figures seen from the left side. (1) animal removed from its shell; a probe g passed into 
the infra-branchial chamber through the excurrent siphonal notch. (2) view from the ventral 
surface of Anodonta, with its foot expanded and issuing from between the gaping valves. (3) 
the left mautle-flap reflected upwards so as to expose the sides of the body. (4) diagrammatic 
sagittal section of Anodonta to show the course of the alimentary canal. (5) the two gill-plates 
of the left side reflected upwards, so as to expose the fissure between foot and gill where the 
probe g passes. (6) diagram to show the positions of the nerve ganglia, heart, and kidney. a, 
centro-dorsal area ; b, margin of the left mantle-flap ; c, margin of the right mantle-flap ; d, ex- 
current (anal) siphonal notch of the mantle-margin ; e, incurrent (branchial) siphonal notch ; Jf, 
foot ; g, probe passed into the superior division of the sub-pallial chamber through the anal 
siphonal notch, and issuing by the side of the foot into the infra-branchial chamber ; h, anterior 
adductor muscle ; i, anterior retractor muscle of the foot ; k, protractor muscle of the foot; J, 
posterior adductor muscle; m, posterior retractor muscle of the foot ; n, anterior labial palp ; 
0, posterior labial palp ; p, base-line of origin of the reflected mantle-flap from the side of the 
body ; q, left external gill-plate ; 7, left internal gill-plate ; rr, inner lamella of the right inner 
gill-plate ; 7.9, right outer gill-plate ; s, line of concrescence of the outer lamella of the left outer 
gill-plate with the left mantle-flap ; t, pallial tentacles ; wv, the thickened muscular pallial margin 
which adheres to the shell and forms the pallial line of the left side; v, that of the left side; w, 
the mouth; 2, aperture of the left kidney, exposed by cutting the attachment of the inner 
lamella of the inner gill-plate ; y, aperture of the genital duct; 2, fissure between the free edge 
of the inner lamella of the inner gill-plate and the side of the foot, through which the probe g 
passes into the supra-branchial chamber ; aa, line of concrescence of the inner lamella of the 
right inner gill-plate with the inner lamella of the left inner gill-plate ; ab, ac, ad, three pit-like 
glandular depressions in the median line of the foot; ae, left shell-valve ; af, space occupied by 
the liver ; ag, space occupied by the gonad ; ah, muscular substance of the foot ; ai, opening of 
bile-duct into the stomach ; ak, stomach; al, rectum traversing the ventricle of the heart ; am, 
pericardium ; an, glandular portion of the left kidney ; ap, ventricle of the heart ; aq, auriculo- 
ventricular orifice ; a7, non-glandular portion of the left kidney ; as, anus ; at, reno-pericardial 
orifice ; au, pore joining the two parts of the kidney ; av, internal pore of the kidney leading to 
the external pore x; aw, left cerebral ganglion ; az, left pedal ganglion; ay, left otocyst; az, 
left visceral ganglion; bb, floor of the pericardium, separating that space from the kidney. 
(After Lankester.) 
