EXPLANATION TO PLATE IV. 



FIG. I. Mytilus californianus. Dorsal view. I, posterior mantle nerve ; 2, bran- 

 chial nerve ; 3, nerve to posterior adductor muscle ; 4, nerves to dorsal body wall 

 and pericardium ; 5, nerves to base of auricles ; 6, nerves to body wall and pericar- 

 dium ; 7, nerves passing posteriorly in the dorsal body wall; 8, 9, 10, ganglia on 

 nerves 4; II, nerves from the cerebro-visceral commissure to the kidneys; 12, 

 nerves from the cerebro-visceral commissures to the adductor muscles of the foot and 

 the byssus. 



FIG. 2. Mya arenaria. Ventral view, i, nerve to mantle and siphon; 2, bran- 

 chial nerve ; 3, nerve plexus on the ventral surface of the kidney between the cere- 

 bro-visceral commissures and the visceral ganglion ; 4, nerves to kidney (and heart) ; 

 5, nerves from the cerebro-visceral commissure to the reproductive glands ; 6, nerves 

 to kidney. 



FIG. 3. Mya arenaria. Lateral view. I, nerve to mantle and siphon; 2, nerve 

 to posterior adductor muscle, dorsal body wall and pericardium ; 3, branch to kid, 

 ney ; 4, branch to posterior aorta and hind gut. 



FIG. 4. Tapes staminea. Ventral view. I, posterior mantle nerves ; 2, siphonal 

 nerves ; 3, nerves to posterior adductor muscle ; 4, nerves toosphradium and gill ; 5> 

 reno-cardiac nerves. 



FIG. 5. Platydon cancellatus. Ventral view. I, nerves to siphon and mantle; 

 2, nerves to osphradium and gill ; 3, nerves to renal organ and heart ; 4, ganglia at 

 the base of the auricles. 



FIG. 6. Cryptochiton stelleri. Ventral view. I, nerves from pleuro-visceral cords 

 to auricles ; 2, nerves that can be followed to the point of attachment of the auricles 

 to the body wall ; 3, 4, connectives between the nerve cords. 



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