/«./?• f 



wrl.12 



Fig. 15.— Antaeus JluviatUis.—A diagrammatic transverse Bection of 

 the thorax through the twelfth somite, showing the course of the 

 circulation of the blood ( x 3). arb. 1$, the anterior or lower, and 

 arb'. 12, the posterior or upper arthrobranchia of the twelfth 

 somite ; av, afferent branchial vessel ; bcv, branchio-cardiac vein ; 

 bg, branchiostegite ; em, extensor muscles of abdomen; ep, epi- 

 meral wall of thoracic cavity ; ev, efEerent branchial vessel ; /«», 

 flexor muscles of abdomen ; fp, floor of pericardium ; gn. 6, fifth 

 thoracic ganglion ; h, heart ; lig, hind-gut ; iaa, inferior abdominal 

 artery, in cross section ; la, lateral valvular apertures of heart ;Jr,. 

 liver ; mp, indicates the position of the mesophragm by which the 

 sternal canal is bounded laterally ; p, pericardial sinus ; pdb. IS, 

 podobranchia, and plb. If!, pleurobranchia of the twelfth somite ; 

 s^sternal artery ; saa, superior abdominal artery ; sc, sternal canal ; 

 t, testis ; xil., sternum of twelfth somite. The arrows indicate 

 the direction of the blood flow. 



