Plate IX. 



Fig. 36. Diagram of Central Nervous System of Tethys punc- 

 tata (Cuv.), seen from below, after Mazzarelli. 



Fig. 37. Diagram of Central Nervous System of Tethys depilans 

 (Linn), seen from below, after Mazzarelli. 



Fig. 38. Diagram of Central Nervous System of Tethys dacty- 

 lomela (Rang), seen from below. 



Fig. 39. Diagram of Central Nervous System of Tethys cer- 

 vina Dall and Simpson, seen from below. 



The following abbreviations apply to all the figures of this 

 plate : c. g., cerebral ganglia ; p. g., pedal ganglia ; pi. g., pleural 

 ganglia ; /. v. g., left visceral ganglion, fused more or less com- 

 pletely with its fellow, the right parietal ganglion ; o. B., organ of 

 Bohadsch, or hypobranchial gland; ^p., third pedal nerve, 0, its 

 branch anastomosing with the right parietal ganglion, b, its 

 branch to the organ of Bohadsch, c, its branch or branches to the 

 muscles of the body wall, in, also in figs. 38 and 39 anasto- 

 mosing with the recurrent branch, 2c, of the second nerve, /. v. 2, 

 from the left visceral ganglion ; 2a, hepatic branch of second vis- 

 ceral nerve, 2h, its main trunk to siphon and anus. 



