114 



THE BIOLOGY OF MARINE ANIMALS 



large ganglion cells of the middle cardiac segments and is relayed via the 

 smaller neurones to the heart muscle. When the median nerve cord is 

 progressively removed the amplitude of contractions diminishes, and when 



Fig. 3.17. Nervous System in the Dorsal Wall of the Heart of 



Palinurus vulgaris 



N. dors, dorsal cardiac nerve piercing the heart wall; Os, ostium; Tr. gang, ganglionic 

 trunk with its nerve cells (from Alexandrowicz, 1932.) 



the longitudinal nerves are cut through, the beating of anterior and 

 posterior regions of the heart becomes asynchronous. Local warming and 

 excitation are most effective in altering heart rate when applied to the 

 central segments of the ganglion. It is of interest that a deganglionated 

 heart, which has ceased beating, may be stimulated into activity by 



