CARDIAC INHIBITION IN DECAPOD CRUSTACEA 145 



Fig. I. Diagram of cardiac ganglion in situ and regulator fibers (Homanis anicri- 



caniis). CG, cardiac ganglion; CNS, subesophageal ganglia; DN, dorsal nerve. 



Arrows indicate usual position of extracellular recording electrodes. So/id line 



represents inhibitor fiber; dashed lines, accelerator fibers. 



vital for all burst activity (Maynard, 1955). Other functions of the small cells 

 are as yet unknown. Synaptic and electrotonic connections exist between the 

 ganglion neurons, the former presumably in the "neuropile" areas and 

 around the large anterior neuron somata (Fig. 3). In addition to collaterals 

 entering the neuropile and axons extending into the myocardium, cardiac 

 neurons send out processes which branch profusely in a limited area of the 

 myocardium beside the ganglion trunk. These are the dendritic arborizations 

 which presumably function as stretch receptors (Isquierdo, 1931 ; Alexandro- 

 wicz, 1932; Bullock et al. 1954). 

 11 



