NATURAL HISTORY OF THE SHIP-WORMS. 227 
EXPLANATION OF PLATES. 
KEY TO LETTERING. 
Anus. 
Anterior adductor muscle. 
Anal canal. 
Anterior ganglion. 
Anterior aorta. 
Posterior aorta. 
Posterior adductor muscle. 
Adductor muscle of palette. 
Afferent renal vein. 
Auricle. 
Afferent branchial vein 
Efferent branchial vein. 
Branchial nerve. 
Blood space of gill lamina. 
Byssus. 
Branchial groove. 
Cerebral ganglion. 
Cerebral commissure. 
Crystalline style. 
Czecum of stomach. 
Secondary czecum of stomach. 
Cephalic hood of mantle. 
Collar 
Cerebro-pedal connective. 
Cerebro-visceral connective. 
Duct of the gland of Deshayes. 
Dorsal artery. 
Dorsal pivotal knob of the shell. 
Epibranchial cavity. 
Epibranchial canal. 
Exhalent or anal siphon. 
Foot. 
Frontal cells of gill. 
Ctenidium or gill. 
Anterior gill filaments. 
Ascending limb of gill filament. 
Descending limb of gill filament. 
Genital duct. 
Gland of Deshayes. 
Gland cells of epidermis. 
Genital organ. 
Intestine. 
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Inter-filamentar junction of gill. 
Inter-laminar spaces of gill. 
Inhalent or respiratory siphon. 
Kidney. 
Afferent tube of kidney. 
Efferent tube of kidney. 
Liver. 
Lateral cells of gill. 
Liver duct. 
Latero-frontal cells of gill. 
Shell ligament. 
Mantle. 
Mantle cavity. 
Mantle groove. 
Muscle fibers. 
Mouth. 
(Esophagus. 
Osphradial nerve. 
Osphradium. 
Otolithic vesicle. 
Ovary. 
Pedal ganglion. 
Pallet. 
Pericardial cavity. 
Gland cells of foot. 
Pleural ganglion. 
Pallial nerve. 
Protractor muscle of pallet. 
Rectum. 
Retractor muscle of pallet. 
Respiratory ganglion. 
Retractor muscle of pallet. 
Stomach. 
Shell. 
Supporting rod of gill filament. 
Sheath of crystalline style. 
Visceral ganglion. 
Valve of anterior end of ventricle. 
Velar cavity. 
‘Ventricle. 
Ventral pivotal knob of the shell valve. 
Visceral mass. 
