136 PATTEN AND REDENBAUGH. [Vol. XVI. 



The chilarial and opercular nerves (Pis. VI-VIII and X, Figs. 

 1-3, 11, and 12, n.ny and n.n.^) arise from the neural side of 

 this portion of the brain and pass backward through the occipital 

 ring to their respective appendages. Mandibular nerves are 

 absent, and the ento-coxal nerves are so modified as not to be 

 recognizable as such. 



The haemal nerves {Ji.nP and hji^) arise from the haemal 

 side of the brain and pass backward through the occipital ring 

 and outward to the sides of the carapace. Intestinal branches 

 {i.nP and i.7i.^) arise at some distance from the bases of the 

 haemal nerves, and cardiac branches {s.c.nJ and s.c.nF) arise 

 still farther out. 



It is worthy of notice that the cardiac branches of these two 

 neuromeres fuse with each other, give a recurrent branch to 

 the lateral sympathetic, and send a pericardial branch, poste- 

 riorly, in the pericardium ; the latter branch also gives recurrent 

 branches to the cardiac nerves of the five branchial neuro- 

 meres. The fusion of sympathetic nerves in this region is of 

 the utmost importance, as it supports in a most satisfactory 

 manner the suggestion of Dr. Patten that we have here, in 

 both scorpions and Limulus, the beginnings of a vagus region. 



The neural and haemal nerves of the accessory brain, together 

 with the ventral cord, pass through the occipital ring. 



b. The Ventral Cord. 



This portion of the central nervous system consists of five 

 paired branchial ganglia and three paired post-branchial gan- 

 glia (Text-figs. 6 and 18, a.gJ^'^), united by two longitudinal 

 connectives. The double nature of the ventral cord is not 

 apparent unless the ensheathing artery is removed. 



The first five branchial ganglia {a.g.'^^^) are separate, but the 

 three post-branchial ganglia {a.gJ'^~'^) are intimately united with 

 one another. The first three abdominal ganglia lie just in 

 front of the corresponding abdominal endochondrites (Text-fig. 

 6, a.eP ; Pis. VI and VIII, Figs, i, 3, and 4, a.ep-") ; the fourth 

 and fifth {a.g.'^-'^) lie in front of the next endochondrite {a.e.") ; 

 the three fused terminal ganglia {a.g/'^-'^) lie considerably in 



