31 

 PLATE XVI. 



THE FRESH- WATER MUSSEL. 



GENERAL STRUCTURE OF BODY 



FIG. 1, . SIDE VIEW OF ANIMAL when left valve and left mantle-lobe are removed 



Mouth, anterior. 



Anus, posterior. 



Heart, dorsal. 



Foot, ventral. 



Gills, lateral, inner and outer. 



Labial palps, two on each side of month. 



Adductor muscles, anterior and posterior, for closing the shell 



Right lobe of mantle, lateral. 

 FIG. 1, b. DORSAL VIEW OF ANIMAL, partly dissected 



Heart. 



Pericardium. 



Vena cava in floor of pericardium. 



Organ of Bojanus beneath pericardium. 



Intestine entering pericardium. 

 DIAG. 1. TRANSVERSE SECTION OF ANIMAL 



Mantle-lobes, right and left, lateral extensions of the dorsal integument. 



Outer gill made up of two lamellae. 



Inner gill made up of two lamellae. 



Foot, median. 



Pericardium. 



f Ventricle. 

 Heart > T, . , 



( Iwo auricles. 



Intestine piercing ventricle. 

 Vena cava. 



Organ of Bojanus, beneath pericardium. 

 ALIMENTARY AND NERVOUS SYSTEMS 



FIG. 2, a. ALIMENTARY SYSTEM Mantle and gills removed on left side, and coiled intestine dissected 



out in foot. 



Mouth, below anterior adductor. 

 Gullet. 

 Stomach. 



Intestine, with neural flexure. 

 Anus, above posterior adductor. 

 FIG. 2, a and b. NERVOUS SYSTEM DISSECTED OUT 



Cerebral or cephalic ganglia, two at base of labial palps. 

 Pedal ganglia, two united and embedded in foot. 

 , Pari'eto-splancliuic ganglia (L. parietes, walls ; Gr. ftplanclma, the entrails), beneath posterior 



adductor. 



Commissures uniting pedal and parieto-splanehnic with cerebral ganglia. 

 SENSE ORGANS 



FIG. 3. Cyclas cornea, a fresh-water form belonging to the same natural order as Anodon, in the foot 



of which the auditory organ can be conveniently examined under the microscope. 

 FIG. 4. AUDITORY ORGAN OF CYCLAS 



Auditory sac lined with ciliated cells and containing fluid and an otolith in the centre. 

 Auditory nerve from pedal ganglion (not shown). 

 CIRCULATORY AND RENAL SYSTEMS 



FIG. 5. THE ORGAN OF BOJANUS dissected from left side, left auricle turned up 



J Auricles receiving blood from gills. 

 Ventricle with anterior aorta aud posterior aorta distributing blood to 

 the body. 



