No. I.] STUDIES ON LIMULUS. 177 



by two separate roots, and the seventh has been observed to 

 pass through the endocranium by two foramina. 



They commingle in a rich plexus supplying the longitudi- 

 nal abdominal muscles. From this plexus numerous branches 

 emerge and, after ramifying and anastomosing through the tis- 

 sues outside of the intestine, enter its walls, some of them 

 extending far forward toward the anterior end. 



The intestinal nerve {i.n.^) arising from the second haemal 

 nerve (Text-fig. 8; Pis. VIII and X, Figs. 3, 11, and 12) 

 passes median to the anterior cornua of the endocranium and 

 supplies the tergo-proplastral muscles [t.p.m."^'^^^), but no 

 branch has been observed going to the intestine. As it has an 

 origin similar to that of the other intestinal nerves, and supplies 

 similar muscles, it has been included in the same category. 



Summary. 



1. The nervous system of Limulus is made up of sixteen 

 neuromeres exclusive of the fore-brain. 



2. Each neuromere consists of a pair of ganglia united by 

 several cross-commissures, a pair of neural and a pair of haemal 

 nerves. In the first or cheliceral neuromere we have in addi- 

 tion a pair of stomodaeal and three rostral nerves. In the 

 three post-branchial neuromeres the appendages and, conse- 

 quently, the neural nerves are absent. 



3. Each neuromere, as a rule, innervates one metamere ; the 

 neural nerves and their branches supply the appendages and the 

 haemal nerves supply the remainder or body portion of the meta- 

 mere, including the epidermis and internal organs. 



But there are many cases in which nerves extend through 

 several metameres either as single nerves or united with others 

 to form longitudinal connectives. For example, the pericardial 

 nerve springs from the fused seventh and eighth neuromeres 

 and communicates with the corresponding nerves of the next 

 five posterior neuromeres. The nerves which supply longitu- 

 dinal muscles extending through several metameres and having 

 muscular slips attached in each of the metameres are united 

 into longitudinal anastomosing plexuses. The lateral sympa- 



