234 THEODORE H. BULLOCK 



Fig. 1. Low magnification view of the whole visceral ganglion of Aplysia cali- 

 fornica. Note thick connective tissue on lower left, true neuropile with giant and 

 small fibers in center, cross section of the base of a nerve just above this, small 

 and large ganglion cells around the outside. Fixative: Flemming's strong; stain: 

 Masson trichrome; calibration: 0.5 mm. 



chromatin-rich and plasma-poor — are present. The giant cells grade con- 

 tinuously into the large and intermediate sized cells (Fig. 2). The largest giant 

 cells in Aplysia californica of about 20 cm relaxed length (approx. 275 g) 

 are about 400 micra; in A. voccaria of 25 cm, 800 micra. Certain ones are dis- 

 tinctive and usually recognizable individually by their size and position. 

 Groupings of cells have been described by Arvanitaki and Tchou (1942). 

 Abundant glia cells are found, especially as thick capsules around the largest 

 cells and massive sheaths around the larger nerve fibers in the tracts, nerves 

 and connectives. The outer connective tissue coat around the nerves and 

 connectives is extremely thick and that around the gangUon is also in many 

 places. 



A special feature of the giant cells and fibers which I want to illustrate in 

 particular is the enormous increase in surface area in certain places. Most of 

 the largest cell bodies are extensively invaded by strands and trabeculae of 

 glial cells. The appearances shown in Figs. 2, 3, 4 and 5 are no doubt equivalent 

 to the trophospongium seen by Holmgren (1902) and other early authors in 

 crayfish, snail and other cells. It is confined in Aplysia giant cells to the inner 

 or axonal side. The cytoplasm of the axon is markedly different in texture and 

 staining affinities from that in most of the soma and extends broadly into the 



