NERVOUS SYSTEM. INVERTEBRATA. 53 



the mantle and respiratory organs, the fourth enters the 

 visceral mass and is distributed to the genital organs. 

 The pedal ganglia are united by two distinct commissures ; 

 each gives off a large handle of nerves to the foot. 



The entire central system is enclosed in a thick sheath 

 of connective tissue (fig. 18). There are two distinct kinds 

 of ganglion-cells large unipolar cells, some of immense 

 size (*17 mm.) situated around the suboesophageal and 



Fig. 18. 



m 



,111 i 



**' >:^;^|:f 



"* ~ * -' 



Horizontal section through the right Cerebral Ganglion of Helix pomatia. 



x40. 



C.T. Connective tissue. G.C. Large ganglion-cells. G.N. Ganglionic 

 nuclei. T.L. Tentacular lobe. 



buccal ganglia and on the posterior surface of the cerebral, 

 and small cells with a minimum of protoplasm, very similar 

 to the ganglionic nuclei of Arthropods, crowded together 

 upon the lateral surface of the tentacular lobes of the 

 cerebral ganglia. The neuropile of the tentacular lobes 

 derived from these cells is peculiarly dense. 



In the upper (isolated) specimen blue paper has been 

 placed beneath the four nerves that rise from the visceral 

 loop, and in the lower specimen the main features of the 

 nerve distribution have been indicated by black paper. 



0. C. 1305 A a. 



Nabias, Act. Soc. Linn. Bordeaux, ser. 5, t. vii. p. 10. 



