THE VOYAGE OF H.M.S. CHALLENGER. 



Fig. 13. — Diagrammatic longitudinal section of Ascidia, showing the heart, the blood-vessels, the branchial sac, 

 the alimentary canal, &c, from the left side. 



br.si., branchial siphon ; at. si., atrial siphon ; t., test ; m., mantle ; br.s., branchial sac ; p.br., peribronchial cavity ; cl., cloaca ; n.g., 

 nerve ganglion ; tn., tentacle ; gl., neua'al gland ; ce.a., oesophageal aperture ; st., stomach ; £., intestine ; r., rectum ; a., anus ; ov., 

 genital organs ; g.d., genital ducts ; h., heart; c.sp., cardio-splanchnic vessel ; v.t., vessel to the test; t.k., terminal knob on vessel 

 in test ; v.t'., vessel from the test ; v.st., vessel to the stomach, &c. ; r.m., vessel to the mantle ; v.m'., vessel from the mantle ; d.v., 

 dorsal vessel ; tr., transverse vessel of branchial sac ; l.v., fine longitudinal vessel of branchial sac ; sg., stigmata of branchial sac ; 

 v.v., ventral vessel ; br.c, branchio-cardiac vessel ; sp.br., splanchuo-branchial vessel. 



