No. I.] STUDIES ON LIMULUS. 141 



which runs longitudinally in the areolar tissue alongside the 

 heart. The distal end of the cardiac nerve communicates 

 with the median nerve (m.c.n.) of the heart. 



The main or integumentary branch {in.n.) of the haemal nerve 

 passes outward into the lateral expansions of the carapace. 



(2) The Cephalic or Cranial Neuromere . — In the cephalotho- 

 rax the typical neuromere (Fig. 9) is somewhat modified. The 



Fig. 9. — Diagram of a typical cranial neuromere. 



br.g., ganglion forming part of the brain; c.c, cross-commissures; e.n., ento-coxal nerves ; 

 e.p.n., external pedal nerve ; h., haemal branch of integumentary nerve ; h.n., haemal nerve ; 

 J. «., intestinal nerve; z«.«., integumentary nerve; z'./.«., internal pedal nerve; m.n., man- 

 dibular nerves; m.c.n., median cardiac nerve; «., neural branch of integumentary nerve; 

 «.«., neural nerve; /.«., pericardial nerve; s.c.n., segmental cardiac nerve; int., nerve to 

 intestine; l.a.tn., nerve to longitudinal abdominal muscles. 



two ganglia are more or less separated, and the cross-commis- 

 sures are in some cases very long. 



The ganglia of the successive neuromeres are crowded 

 together, so that the neural and haemal nerves appear to arise 

 from the neural and haemal sides, respectively, of the ganglia, 

 instead of from the posterior and anterior sides. 



The neural nerve («.«.) arises from an enormous ganglion, 

 which in the adult is much obscured by the thick membranes 



