ev: A Sa (\-32 
pM : y \ Y\plb.12 
Lk \ NIN J jI-09. 
bg: 
fi : 
sd. aon 
Fig, 15.—Astacus fluviatilis—A diagrammatic transverse section of 
the thorax through the twelfth somite, showing the course of the 
circulation of the blood (x 3). arb. 12, the anterior or lower, and 
arb’, 12, the posterior or upper arthrobranchia of the twelfth 
somite ; av, afferent branchial vessel ; bev, branchio-cardiac vein ; 
bg, branchiostegite; em, extensor muscles of abdomen; ep, epi- 
meral wall of thoracic cavity; ev, efferent branchial vessel; fm, 
flexor muscles of abdomen ; /, floor of pericardium ; gz. 6, fifth 
thoracic ganglion ; h, heart ; 4g, hind-gut ; iaa, inferior abdominal 
artery, in cross section ; da, lateral valvular apertures of heart ; /7, 
liver ; mp, indicates the position of the mesophragm by which the 
sternal canal is bounded laterally ; », pericardial sinus; pdb. 12, 
podobranchia, and plb. 12, pleurobranchia of the twelfth somite ; 
sa,sternal artery ; saa, superior abdominal artery ; sc, sternal canal ; 
t, testis; XII., sternum of twelfth somite. The arrows indicate 
the direction of the blood flow. 
