84 



THE FEESHWATER MUSSEL 



B. The Gills, 



Cut away the right mantle-lobe completely with scissors, 

 cutting along the base of the palps, round the anterior end of 

 the gills, and back along the attached base of the outer gill. 

 Take care not to damage the parts to which the mantle is 

 attached. 



Each gill consists of a pair of lamellae, united along their 

 ventral borders. Each lamella is formed of very numerous 

 vertical and horizontal bars, united to form a kind of trellis- 



PR 



RN N K V AU B PC R H 



AR 



AA 



Id VM OP IP PQ. 



FIG. 19. Anodonta cygnea. Diagrammatic view from the right side 

 The right valve of the shell and the right mantle-lobe have been 

 removed, and the pericardial cavity opened from the right side. 

 The line of attachment of the right mantle-lobe is indicated by the 

 strong dotted line. (A. M. M.) 



A, margin of the left valve of the shell in which the animal is lying. 

 AA, anterior adductor muscle. AN", anus. AR, right anterior retractor 

 muscle. AIT, right auricle. B, ligament of the shell. C, cloacal cavity. 

 CO-, right cerebral ganglion. D, partition between the inhalent and exhalent 

 apertures. E, tentacles bordering inhalent aperture. F, foot. H, anterior 

 aorta. IQ-, inner gill of right side. IP, inner labial palp of right side. 

 K, kidney. LM, left mantle-lobe. M, mouth. M", posterior aorta. OG, outer 

 gill of right side. OP, outer labial palp of right side. P, right protractor 

 muscle. PA, posterior adductor muscle. PC, pericardial cavity. PG, right 

 pedal ganglion. PR, right posterior retractor muscle. R, rectum. RM, line 

 of attachment of right lobe of mantle. RN, space between right and left 

 lobes of mantle above the posterior adductor muscle. V, ventricle. VM, vis- 

 ceral mass. "VVj edge of left mantle-lobe. 



