No. I.] STUDIES ON LIMULUS. ii 



The brain forms a close-fitting collar around the oesophagus 

 and lies a little in front of the center of the plastron. Six 

 pairs of large pedal nerves radiate from the neural side of the 

 collar and innervate the six pairs of thoracic appendages. Six 

 pairs of integumentary nerves belonging to the same neuro- 

 meres radiate from the haemal side and innervate the skin 

 and other organs on the haemal and neural sides of the 

 carapace. 



In PI. I, Fig. 3, only the posterior half of the collar is repre- 

 sented ; n.nA, n.n.S, and n.n.^ are the three posterior pedal or 

 neural nerves of the thoracic neuromeres ; h.nA, h.n.S, and 

 hji.^ are the three integumentary or haemal nerves of the 

 same neuromeres. Of these, the haemal nerves {h.n.^), which 

 belong to the same metamere as the sixth pair of legs, give off 

 small branches (in.n.^) which pass through foramina (/. ') in the 

 plastron and communicate with a sympathetic system supplying 

 the intestine and the longitudinal abdominal muscles. The 

 main portions of the nerves give off branches to the region 

 of the heart, and then ramify over the skin of the haemal and 

 neural surfaces of the cephalothorax. 



The ventral cord {v.c), the chilarial {n.n.7), and the opercular 

 (n.n.^) nerves, and two pairs of integumentary nerves (A.n.7 and 

 hji.^) belonging to the chilarial and opercular neuromeres, pass 

 out from the posterior side of the brain through the occipital 

 ring. 



The chilarial nerves {n.n.T , Figs. 3 and 4) arise on the neural 

 side of the posterior end of the oesophageal collar and pass 

 directly backwards through the occipital ring close to its neural 

 portion and innervate the chilaria. 



On the haemal side of the collar arise a pair of integumentary 

 or haemal nerves {h.nJ, Figs. 3 and 4) belonging to the chilarial 

 neuromere. They diverge laterally and pass through the occip- 

 ital ring, sending branches iin.n.7) through foramina {/.-) to 

 supply the intestine and the longitudinal abdominal muscles. 

 The main portions of the nerves bend sharply outwards after 

 leaving the occipital ring, and, after giving off cardiac branches, 

 supply the skin on the haemal and neural surfaces of the ante- 

 rior portion of the abdomen. The chilaria, though apparently 



