CONTENTS xi 



PAGE 



1. The Aeeas of Innervation of the taeious Ganglia . 133 



2. Origin of the Crossing of the Pleuroviscbral Con- 



nective (Chiastoneury) . . . 135 



3. Special Remarks on the Nervous System of the Gas- 



tropoda . . . . 137 

 0. scaphopoda . .142 



D. Lamellibranchia . . . 143 



E. Cephalopoda . . .146 



XIV. An Attempt to Explain the Asymmetry of the Gastropoda 149 



XT. The Sensory Organs . 162 



A. Integumental Sensory Organs 162 



1. Tactile Organs . .162 



2. Olfactory Organs . . 162 



3. The "Lateral Organs" of the Diotooardia 165 



4. Gustatory- Organs . . 166 



5. Subraddlar Sensory Organ of Chiton . . 166 



6. The Sensory Organs on the Shell of Chiton . 166 



B. Auditory Organs 167 



C. Visual Organs . 169 



1. Optic Pits 169 



2. Optic Vesicles or Vesicular Eyes . 170 



3. The Eye of the Dibranchiate Cephalopoda . . 170 



4. The Dorsal Eyes of Oncidium and the Eyes at the 



Edge of the Mantle in Pecten 173 



5. The Eyes on the Shell of Chiton . 175 



6. The Compound Eyes op Arca and Pectunoulus 175 



7. Degeneration of the Cephalic Eyes . 176 



XVI. The Alimentary Canal . . 176 



A. Buccal Cavity, Snout, Proboscis 178 



B. The Pharynx and Jaws, the Tongue and Salivary 



Glands .... • 180 



Formation of the Radula 183 



C. The (Esophagus . 187 



D. The Mid-gut with the Stomach and Dige.stive Gland 



(Liver) . . 190 



1. Amphineura . • 191 



2. Gastropoda 192 



3. ScAPHOPODA . . 193 



4. Lamellibranchia 194 



5. Cephalopoda ISA 



E. Hind-gut (Rectum) • 195 



XVII. The Circulatory System . 198 



A. General . 198 



