No. I.] STUDIES ON LIMULUS. 1 37 



front of the last endochondrite (a.e/^), which belongs to the fifth 

 branchial metamere. 



The five branchial neuromeres are typical neuromeres, each 

 with its double ganglion and cross-commissure, and -neural and 

 haemal pairs of nerves (Text-fig. 8). The neural nerves (Text- 

 figs. 6, 8, and 12 ; Pis. VI, VIII, and IX, Figs, i, 3, 4, and 6, 

 n.nP''^) arise from the posterior end of the ganglion and give off 

 intestinal branches {i.nS''^) close to their origins. The cardiac 

 branches (s.c.n.')'^^) communicate with the lateral sympathetic 

 (/.s.n.) and with the pericardial nerve (/.«.) by recurrent 

 branches. 



The post-branchial neuromeres are not well defined. The 

 ganglia are closely fused together, and the neural nerves are 

 absent. 



The haemal nerves (/i.n/^~^^) of all three neuromeres give 

 off intestinal branches (t.n/'^~^^), and post-cardiac branches 

 {s.c.n/'f^''^), which have a distribution similar to the cardiac 

 branches, are given off from the first two post-branchial nerves. 

 However, as the heart does not extend into the post-branchial 

 metameres, the post-cardiac nerves do not communicate with 

 this organ. 



2. Peripheral Nervous System. 

 a. Nerves frojn the Fore-Brain. 



Six nerves have been found arising from the fore-brain, three 

 olfactory, one median eye, and two lateral eye nerves. These 

 are all accompanied by blood vessels, but there are other blood 

 vessels given off from the same region, which do not accompany 

 nerves and which might easily be mistaken for nerves in a 

 hasty dissection. This fact probably accounts for the varied 

 number of nerves found by different investigators. 



(i) Olfactory Nerves. — Owen, Milne-Edwards, and Packard 

 have described two integumentary nerves arising from the 

 anterior side of the fore-brain. Patten described three nerves, 

 and showed that they had a most remarkable development and 

 that they supplied an aggregation of sense buds on the 

 under surface of the carapace in the median line, anterior to 



