No. I.] 



STUDIES ON LIMULUS. 



121 



&\r 



Fig. 5. — Diagram showing the muscles and distribution of the nerves in the operculum. The oper- 

 culum is flexed upon the abdomen, and is seen from the neural side (about i}^ natural size). 



<z.e., abdominal endochondrite of opercular segment; 5. c. 7, 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 ; pv., oviduct. 



Muscles: a.b.tnfi, abductor muscle of operculum; b.t.tn., branchio-thoracic muscles; 

 e.b.tn.^, external branchial muscle; ib.iii., internal branchial muscle; iJ.iii,, muscle of inner 

 lobe; £>./.?«., muscle of outer lobe. 



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

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

 itt.n.'^ and 8, integumentary branches of haemal nerves of chilarial and opercular neuromeres ; 

 /.(?.«., internal branch of opercular nerve; l.s.n., lateral sympathetic nerve; w^.^j.?/., median 

 branch of opercular nerve; ti.n.^, neural or opercular nerve; s.c.ii7 ^nA^, fused segmental 

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



