No. I.] 



STUDIES ON LIMULUS. 



157 



Fig. 



15. — Diagram showing the muscles and distribution of the nerves in the operculum. The 

 operculum is flexed upon the abdomen, and is seen from the neural side fabout i>^ natural size). 



a.e., abdominal endochondrite of opercular segment ; bxP, capsuliginous bar or branchial 

 cartilage of chilarium ; b.c.'^, branchial cartilage of operculum ; endo., endocranium ; i.L, inner 

 lobe of operculum ; oc.r., occipital ring ; o.l., outer lobe of operculum ; o.v., oviduct. 



Muscles : a.*. w.^ abductor muscle of operculum; b.t.m., branchio-thoracic muscles; 

 e.b.m.^, external branchial muscle ; i.b.tn., internal branchial muscle ; i.l.m., muscle of inner 

 lobe; (?./.?«., muscle of outer lobe. . 1 . , 



Nerves : e.o.n., external branch of opercular nerve; h.tiJ and ^, haemal nerves of chilanal 

 and opercular segments ; i.nj and ^, intestinal nerves of chilarial and opercular neuromeres ; 

 in.nP and 8, integumentary branches of haemal nerves of chilarial and opercular neuromeres ; 

 /.o.«., internal branch of opercular nerve; l.s.n., lateral sympathetic nerve; tn.o.n., median 

 branch of opercular nerve ; n.ti.^, neural or opercular nerve ; s c.n7 and ^, fused segmental 

 cardiac nerves of the seventh and eighth neuromeres ; v.c, ventral cord. 



