Fig. 8. Cross sections of the anterior (Ante: A,B) and posterior (Post: C,D) intestines from freshwater (FW: A,C)- and seawater (SW: B,D)-adapted eels, stained with Hematoxylin and Eosin. In the posterior intestine, both inner circular (c) and outer longitudinal (l) muscle layers were thinner in seawater eel than in freshwater eel, whereas there was no apparent structural difference in the anterior intestine of freshwater and seawater eels. Scale bar, 100 µm.