em. 



la.V- }' 



aTlJ2 



zaa. 



Fig, 15. — Astacus fltiviatilis, — A diagraminatic transverse section of 

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

 circulation of the blood ( x 3). arh. 12, the anterior or lower, and 

 arV. 12, the posterior or upper arthrobranchia of the twelfth 

 somite ; av, afferent branchial vessel ; hcv^ branchio-cardiac vein ; 

 tg, branchiostegite ; em^ extensor muscles of abdomen ; eiy, epi- 

 meral wall of thoracic cavity ; cy, efferent branchial vessel ; fm, 

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

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

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

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

 sternal canal is bounded laterally ; 7;, pericardial sinus ; pdb. 13, 

 podobranchia, and 2^^^. 12, pleurobranchia of the twelfth somite ; 

 4'<2,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. 



