31 



PLATE XVI. 



THE FRESH- WATER MUSSEL. 



General Structuee of Body — 



Fig. 1, a. Side View op Animal when left valve and left iiiaiitle-lobe are removed — 

 Mouth, anterior. 

 Anus, posteriur. 

 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 

 Tiight lobe of mantle, lateral. 

 Fig. 1, h. Dorsal View op Animal, partly dissected — 

 Heart. 



Pericardium. 



Vena cava in floor of pericardium. 

 Organ of Bojanus beneath pericardium. 

 Intestine entering pericardium. 

 Diao. 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 lamelliB. 



Foot, median. 



Pericardium. 



( Ventricle. 

 ( Two 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 h. Nervous System dissected out — 



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



Pedal ganglia, two united and embedded in foot. 



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



adductor. 

 Commissures uniting pedal and parieto-splanchnic with cerebral ganglia. 



Sense Organs — • i <■ ,. 



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. i. Auditory Oi;gan oe Cyclas — 



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

 Auditory nerve from pedal ganglion (not shown). 



CrRCULATOEY AND KeNAL SYSTEMS — 



Fig. 5. The Organ of Bojanus dissected from left side, left auricle turned up— 



( Auricles receiving blood from gills. 

 Heart (Systemic) } Ventricle with anterior aorta aud posterior aorta distributing blood to 

 ( the body. 



