No. I.] STUDIES ON LIMULUS. 165 



the median line to the internal slips of the extensors {t.e.m.'^), 

 and to the epidermis in the median line. Some of the branches 

 go to the posterior margin of the carapace over the base of 

 the caudal spine. Inside the extensor muscles the branches 

 anastomose with those of the first post-cardiac nerve. 



(c) Integumentary Brandies. — Besides the integumentary 

 portion of the post-cardiac, which innervates the epidermis 

 upon the haemal side of the carapace, there is a large integu- 

 mentary branch of the main nerve, which innervates the neural 

 side of the carapace. After giving off the post-cardiac branch, 

 the main nerve enters the flexor muscles of the caudal spine 

 and gives off to these muscles branches which anastomose 

 with similar branches from the third post-branchial nerve {Ji.n.'^). 

 The integumentary portion turns posteriorly and supplies the 

 epidermis in the posterior angles of the abdominal carapace. 



(3) Nerves of the Third Post-Branchial Neiiromere . — The 

 terminal ganglionic mass sends out a large pair of nerves 

 {h.n.'^), which pass posteriorly upon each side of the rectum 

 to the telson. Each of these nerves divides, sometimes almost 

 at the very base, into two branches. The first goes between 

 the flexor {t.f.m.) and extensor {t.e.m.^) muscles of the telson and 

 gives to the flexor {t.f.m) branches which anastomose with the 

 branches of the second post-branchial nerve. The distal or 

 integumentary portion divides, sending one branch to the pos- 

 terior angle of the carapace, and the othef to the telson. This 

 nerve also sends some fine branches to the epidermis in the 

 posterior margin of the carapace neural to the base of the 

 telson. 



The second branch, which is much the larger of the two, 

 breaks up in the telson into numerous branches. At the side 

 of the rectum it gives off a branch {i.n.'') which supplies the 

 anal muscles and the rectum and communicates with the intes- 

 tinal nerve {i.n.'^) of the second post-branchial neuromere. A 

 branch of this nerve also goes to the epidermis at the base of 

 the telson, posterior to the anus. 



Milne-Edwards describes a small ganglion upon each side of 

 the anus at the root of the nerve going to the rectum, but we 

 have failed to find it. This ganglion is supposed to lie inside 



