ALPHABETICAL EXPLANATION 



Of the Meaning of the Letters in Plates X. and XL 



a, auns 

 au, eye 



b, ventral muscles 



c, gill- cavity 



ch, notochord (spinal axis) 



cl, cloacal cavity 



cs, notochord sheath 



cl, intestinal tube 



do, dorsal wall of the intestine 



du, ventral 



>j 



» 



>j 



A-, gills 



Tea, gill-artery 



I, leather-plate 



lb, liver 



lb', anterior end of the liver 



Iv, liver vein 



m, medullary tube 



Wj, brain-bladder 



