No. I.] 



STUDIES ON LIMULUS. 



123 



Fig. 6. — Diagram showing the muscles and distribution of nerves in the first gill. The appendage 

 is flexed upon the abdomen, and is seen from the neural side (about iVz natural size). 



a.e!i, abdominal endochondrite ; b.c.^ and 9, branchial cartilages of operculum and first gill ; 

 :./., inner lobe of gill ; ?«./., median lobe of gill ; c.L, outer lobe of gill. 



Muscles: a.b.m^, abductor muscle of gill; b.t.m., branchio-thoracic muscles; e.b.tn^, 

 external branchial muscle; i.b.m.'), internal branchial muscle; i.l.m., inner lobe muscles; 

 l.a.m., longitudinal abdominal muscles; o.l.m., outer lobe muscles. 



Nerves: a.e:., first abdominal ganglion; e.b.n., external branch of neural nerve; ^.«., 

 branch of neural nerve supplying gill book; /;.«.9, haemal nerves; i.b.n., internal branch cf 

 neural nerve ; /.«.9, intestinal nerve (two branches are shown, a posterior and an anterior one) ; 

 /'«.«.9, integumentary branch of haemal nerve ; /.j^.«., lateral sympathetic nerve ; m.b.n., median 

 branch of neural nerve ; n.n.^, neural nerve ; s.c.n.'}, segmental cardiac nerve ; v.c, ventral cord. 



