No. I.] STUDIED ON LIMULUS. 153 



branches and the median nerve {tn.e.n.) of the heart, it is very 

 probable that such a connection exists. The connective-tissue 

 strands supporting the heart in this region are numerous, 

 rendering it very difficult to distinguish nerve fibers and trace 

 them through the mass of other fibers. 



In the second, third, and fourth thoracic neuromeres no car- 

 diac branches have been found ; in the fifth a small nerve was 

 found which corresponded in origin to the cardiac branches 

 of the other haemal nerves, but its distribution could not be 

 traced out. 



(c) Integumentary Branches. — The haemal nerve becomes 

 enlarged and flattened near the outer margin of the entocoxite 

 and forms the integumentary nerve (Text-figs. 9, 1 1, and 12 ; Pis. 

 VI and VII, Figs, i and 2, in.n). It then divides into two 

 main branches, one (;/.) going to the neural surface of the cara- 

 pace, and the other (//.) to the haemal surface. 



The neural branch soon divides into two more branches, and 

 these break up into numerous fibers, which ramify over the 

 neural surface of the carapace and supply the skin, and prob- 

 ably the numerous muscle strands passing between the two 

 surfaces of the lateral expansions of the carapace. 



The haemal branch gives off near its origin a small nerve, 

 which turns haemally toward the median line, and supplies 

 the epidermis of the haemal side between the pericardium and 

 the outer edges of the entocoxites. In some cases these 

 branches anastomose in the epidermis with the correspond- 

 ing branches of the other haemal nerves. The main haemal 

 branch breaks up into small branches which innervate the skin 

 upon the haemal side of the lateral expansions of the carapace. 



The second haemal nerve {Ji.n.^) is somewhat larger than the 

 others, and its integumentary branches have a larger area of 

 distribution, for they supply the thicker anterior portion of the 

 cephalic shield. It lies almost parallel to the median line, while 

 the sixth one {h.nJ') lies at right angles to it. The interme- 

 diate haemal nerves {h.n.^'^), owing to the rounded form of the 

 cephalothorax and the central position of the brain, necessarily 

 diverge from each other like the radii of a circle. 



Another noticeable feature about the haemal nerves is a 



