THE LAMELL1BRANCHIA 



269 



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FIG. 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 excnrrent siphonal notch. (2) view from the ventral 

 surface of Anodonta, with its foot expanded and issuing from between the gaping valves. (3) 

 the left mantle-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 ; ft, 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 ; /, 

 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 ; I, 

 posterior adductor muscle ; m, posterior retractor muscle of the foot ; n, anterior labial palp ; 

 a, posterior labial palp ; ?>, base-line of origin of the reflected mantle-flap from the side of the 

 body ; q, left external gill-plate ; r, left internal gill-plate ; rr, inner lamella of the right inner 

 gill-plate ; r.g, 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 ; u, the thickened muscular pallial margin 

 wli idi adheres to the shell and forms the pallial line of the left side ; v, that of the left side ; w, 

 the mouth ; x, aperture of the left kidney, exposed by cutting the attachment of the inner 

 lamella of the inner ^'ill-plate ; y, aperture of the genital duct ; z, 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 ; ore, 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 ; a/, 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 ; ar, non-glandular portion of the left kidney ; as, anus ; at, reno-pericardial 

 orifice ; an, pore joining the two parts of the kidney ; av, internal pore of the kidney leading to 

 the external pore x ; aw, left cerebral ganglion ; ax, left pedal ganglion ; ay, left otocyst ; az, 

 left visceral ganglion ; bb, floor of the pericardium, separating that space from the kidney. 

 (After Lankester.) 



