lOO PATTEN AND REDENBAUGH. [Vol. XVI. 



adjacent trunk muscles. The segmental intestinal nerves, like 

 the cardiac nerves, are absent from the anterior five thoracic 

 segments ; therefore the intestinal and the cardiac branches of 

 the sixth, seventh, and eighth nerves having a greater territory 

 to cover are larger and better developed than the corresponding 

 nerves in the trunk region. These enlarged intestinal nerves 

 supply that part of the alimentary canal confined to the thorax, 

 exclusive of the oesophagus and proventriculus, into which the 

 liver ducts open. This part corresponds roughly to the gastric 

 region of vertebrates, and the nerves that supply it may thus 

 be fairly regarded as comparable with the intestinal branches 

 of the vagus, especially since they have their origin in spinal 

 nerves which for other reasons we had regarded as comparable 

 with the system of vagus nerves in vertebrates. 



We thus have in Limulus a complex condition that clearly 

 indicates the initial differentiation of sympathetic and vagus 

 systems similar to those found in vertebrates. This is shown 

 (i) by the presence in Limulus of double longitudinal nerve 

 trunks that form anastomosing plexuses, united on one side 

 by segmental rami communicantes with the spinal nerves, and 

 on the other by segmental cardiac and intestinal nerves with 

 the heart and intestine ; (2) by the absence or great reduction 

 of segmental cardiac and intestinal nerves anterior to the 

 sixth thoracic neuromere ; (3) by the consequent increase in 

 size, and in the territory covered by the intestinal and cardiac 

 nerves of the sixth, seventh, and eighth neuromeres ; (4) by the 

 origin of the enlarged cardiac and intestinal nerves of the 

 seventh and eighth thoracic segments from those spinal nerves 

 which on entirely independent grounds we had long ago regarded 

 as comparable with the vagus group in vertebrates. 



The sympathetic system of Limulus differs from that of 

 vertebrates in the absence of segmental ganglia, although iso- 

 lated ganglion cells are scattered here and there along the 

 main intestinal and cardiac nerves and over the surface of the 

 intestine. 



The division of labor between Mr. Redenbaugh and myself 

 in the preparation of this paper was rather unusual. I began 



