Plate I 



Fig. 3. View of the surface of an unsectioned visceral ganglion o( Aplysiafasciata. 

 The naturally orange pigmented nerve cells are distinguishable. Between them, 

 dark coloured vessels and capillaries are also visible owing to the injection of 

 colloidal Janus green through the dorsal artery. The largest cell visible in this 

 field is the Br cell at the upper left side. A capillary cluster is directly in contact 



with the cell. x60. 



Fig. 4. Thick section (100 /i) through the dorsal side of a fixed, frozen visceral 

 ganglion, stained with methylene blue. The connective tissue is stained blue- 

 mauve; the nerve cells, green-blue. Some giant nerve cells are easily identifiable 

 by their situation relative to the nerve trunks. The latter are not visible on this 

 section. The giant upper cell is a Br cell. The giant A cell is located at the left, 



centre. 11. 



Fig. 5. Frozen, formalin-fixed section through the visceral ganglion stained with 

 methylene blue. The giant cell in the centre is the A cell. The dark blue cytoplasm 

 around the nucleus is the highly basophilic perinuclear cytoplasm. It is sur- 

 rounded by a peripheral, less basophilic cytoplasm. Quite at the periphery lies a 

 thin dark ring of brownish pigment. The connective tissue is metachromatically 

 stained mauve. The giant A cell is always surrounded by numerous smaller 

 "satellite" nerve cells. x32. 



Fig. 6. Section through the A soma, formalin fixed, frozen, thionin stained. 

 This preparation was carried out in order to determine the exact position of 

 the micro-electrode tip after having picked up the electrical activity of the cell. 

 One observes the channel made by the tip of the introduced microelectrode. 

 Even in these conditions the cell exhibited autoactivity for more than two 

 hours. Here the nerves are stained brownish, the glial tissue is metachromatically 



stained red. x30. 



Fig. 7. Vascular net on the A cell. Unsectioned preparation injected with a 

 colloidal solution of Janus green. Crossed vessels on the surface of the A soma. 



60. 



Fig. 8. Section through another A soma, prepared as above, but stained with 

 methylene blue. The hole into the nucleus was opened by the tip of the micro- 

 electrode. This soma had been autoactive for more than 5 hr. A blue ribbon-like 

 structure touching the inferior edge of the brownish pigment layer of the A soma 

 corresponds to the initial segment of another soma, contracting an axosomatic 

 synapse with the A soma. x40. 



Fig. 9. Section of the Br soma, prepared as above. Highly basophilic perinuclear 

 cytoplasm surrounded by a peripheral, less basophilic cytoplasm. Between the 

 two lies a very thin dark layer of brownish pigment. The density of this 

 pigment becomes very high at the left side of the cell in the axon hillock area. The 

 connective tissue is metachromatically stained blue-mauve. x40. 



Fig. 10. Another section of the Br soma. Formalin-sea water fixed preparation, 

 frozen, sectioned, methylene blue-stained and photographed under higher magni- 

 fication. Only a quarter of the section is visible. At the upper right side can be 

 seen a portion of the nucleus surrounded by the highly basophilic perinuclear 

 cytoplasm. Towards the periphery lie dark strands of brownish pigment (these 

 are naturally orange (see Fig. 3) but here altered by the fixation procedure) 

 surrounded at the periphery by some less basophilic cytoplasm. , 300. 



