Spider cardiac physiology, I. Structure and function of the cardiac ganglion

1. 1. Electrophysiological studies into the function of the cardiac ganglion of the spider Eurypelma marxi Simon have shown that the ganglion functions in both the genesis and the co-ordination of the heart-beat. 2. 2. The microanatomy of the cardiac ganglia of two species of spider was studied by light microscopy. In both species the ganglion consists mainly of three nerve components: cell bodies, cell processes, and regions of neuropil. 3. 3. Three types of nerve-cells in the ganglion are recognized. These cell types can be distinguished on the basis of size, shape, number of cel processes, and cytoplasmic detail. 4. 4. From reconstructions made from sections of the ganglion, total numbers of cells, the numbers of each cell type, and the distribution of the cells in the ganglion have been determined.